Benchmarked at one million concurrent WebSocket connections and 30 million delivered messages per minute on a single server, Centrifugo is a self-hosted real-time messaging server that integrates with any backend language — Node.js, Python, Go, Ruby, PHP, Java — without requiring architectural changes to your existing application. It handles persistent connections over WebSocket, HTTP-streaming, Server-Sent Events, gRPC, and experimental WebTransport, routing messages through a channel-based PUB/SUB model with automatic reconnection recovery that replays missed messages from hot channel history. Built-in horizontal scaling operates through Redis (including Redis Cluster, AWS ElastiCache, Valkey, KeyDB, and DragonflyDB), NATS, or PostgreSQL brokers, allowing multi-node deployments without external message queues. The server provides JWT-based authentication using HMAC or RSA keys, granular channel permissions, online presence tracking showing who is currently subscribed to a channel, and an RPC proxy that forwards client calls to your backend over HTTP or gRPC. The embedded ReactJS admin web interface displays real-time connection statistics, node information, and provides an interactive API console for publishing messages, managing subscriptions, and inspecting channel history. Official client SDKs are available for JavaScript, Dart, Go, Swift, and Java, with unidirectional transports requiring no SDK at all. Centrifugo also supports delta updates to minimize bandwidth, connection event proxying, and Prometheus-compatible metrics for Grafana monitoring. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.

Mercure is a realtime hub that pushes updates from your backend straight to browsers over Server-Sent Events, so live dashboards, chat rooms, and activity feeds refresh the moment data changes. Subscribers connect through the browser's built-in EventSource API and choose topics with exact matchers for single resources or URL Pattern matchers for whole families such as /books/:id. Publishers send one form-encoded POST to the hub endpoint, and Mercure fans each update out to every matching connection instantly. JWT access tokens grant publish and subscribe rights topic by topic, so private updates reach only entitled clients while public topics can stay open to anonymous subscribers. If a connection drops, the client reconnects with its last event ID and Mercure replays the updates it missed from stored history. Subscription events announce every arrival and departure, so your application gets live presence and a current list of who is connected. A built-in debug UI shows messages flowing through the hub alongside active subscriptions, turning realtime bugs into something you can watch happen. Optional end-to-end encryption protects sensitive payloads, and any backend able to send an HTTP POST can publish, whatever language it runs. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

An entire backend in a single Go executable: PocketBase embeds SQLite with realtime subscriptions, authentication and user management, file storage, and an admin dashboard, all behind a REST-ish API. SQLite runs in WAL mode, which outperforms client-server databases for the read-heavy workloads typical of small and mid-sized apps. Authentication supports email/password, one-time passwords, and 15+ OAuth2 providers including Google, Apple, and GitHub, with stateless tokens. Clients subscribe to record changes over server-sent events, and official JavaScript and Dart SDKs cover web, mobile, and Flutter frontends. Collections, rules, and API access permissions are managed visually in the admin UI. When you need custom logic, extend it with JavaScript hooks running in the embedded JS VM of the prebuilt binary, or import PocketBase as a Go library and compile custom business logic into your own single-file backend. File storage attaches uploads to records with thumbnail generation for images and optional S3-compatible external storage. All state lives in one pb_data directory, so backup is a directory copy and upgrade is replacing a binary - one of the lowest-maintenance backends you can run. The contrast with Firebase is the point: where usage-based pricing scales with reads, writes, and bandwidth, PocketBase runs the entire backend at flat hosting cost, and the data is a plain SQLite file you can copy anywhere. MIT-licensed.

A PostgreSQL database becomes a production-grade GraphQL API the moment Hasura GraphQL Engine points at it: track tables and relationships - existing schemas included - and full query, mutation, and subscription types appear with where, order_by, limit, offset, and on_conflict arguments, no resolvers or boilerplate written. Its Haskell core compiles GraphQL to efficient SQL, and any query becomes a real-time live query with a single keyword, powering dashboards and collaborative UIs over standard GraphQL subscriptions. Authorization is where Hasura earns its enterprise reputation: role-based access control with row- and column-level permission policies driven by session variables from JWTs, auth webhooks, or headers - each role effectively sees its own GraphQL schema containing only what it may touch, integrating cleanly with Auth0, Firebase, or homegrown auth. Event triggers fire webhooks on inserts, updates, and deletes for asynchronous business logic; Actions extend the schema with custom REST handlers; remote schema stitching merges external GraphQL services into one endpoint; and auto-generated REST endpoints serve clients that skip GraphQL. A browser console handles data modeling and API exploration, the CLI manages migrations and metadata as code, and deployment is a single stateless Docker container beside Postgres.

Kuzzle ships a production-ready backend from day one: data storage with Elasticsearch search, real-time pub/sub notifications, user authentication, role-based permissions, and a multi-protocol API serving HTTP, WebSocket, and MQTT simultaneously on port 7512. Rather than rebuilding these standard features from scratch for each project, you get a ready-made backend that accepts connections from web applications, mobile clients, and IoT devices through one unified API surface. Elasticsearch provides persistent document storage with full-text search, geospatial queries, and aggregation pipelines, while Redis handles internal caching and memory storage operations. The Koncorde real-time engine powers pub/sub messaging and database notifications, enabling clients to subscribe to document changes with filter conditions that trigger instant updates when matching data is created, modified, or deleted. User management includes JWT-based authentication, role-based access control with granular permissions at the controller and action level, and pluggable authentication strategies via Passport.js. The extensible plugin framework allows developing custom business logic, additional authentication providers, storage connectors, and protocol handlers. Client SDKs for JavaScript, Dart, Kotlin, and C++ accelerate frontend development, while the Kourou CLI provides command-line API access and project scaffolding. The Vue.js Admin Console offers a web interface for managing indexes, collections, documents, users, profiles, and roles. Horizontal scaling through masterless cluster mode targets 99.99% uptime without single points of failure. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.

Stateful serverless actors that run indefinitely, sleep when idle, and persist state across restarts without external database round trips. Rivet provides a vendor-neutral alternative to Cloudflare Durable Objects, delivering long-running processes with co-located in-memory state and per-actor SQLite databases on any infrastructure you choose. The Rust engine comprises four packages: Pegboard for actor orchestration, Gasoline for durable execution, Guard for traffic routing via Envoy, and Epoxy implementing multi-region KV storage through EPaxos consensus. Each actor maintains instant-access in-memory state plus a dedicated SQLite database for relational queries, backed by RocksDB on single nodes or PostgreSQL with NATS pub/sub for multi-node clusters. RivetKit SDKs in TypeScript, Rust, and Python support built-in WebSocket connections, task queues, scheduling, and CRDT-based real-time collaboration. The v2.3 rewrite moved the core runtime from JavaScript to native Rust via WebAssembly, eliminating main-thread blocking across Node.js, Bun, Deno, and Cloudflare Workers. A built-in dashboard provides actor inspection with real-time Prometheus metrics. Deploys as a single Docker container on port 6420 with optional PostgreSQL for persistence. Available on RepoCloud with a dedicated VPS under the Apache 2.0 license.

With over 20,000 GitHub stars and adoption by companies building everything from telehealth platforms to AI voice agents, LiveKit is the most widely deployed open-source real-time communication server available. The Go-based Selective Forwarding Unit handles hundreds of concurrent participants per node with adaptive bitrate streaming, simulcast layers, SVC codec support for VP9 and AV1, and end-to-end encryption. Client SDKs span JavaScript, Swift, Kotlin, Flutter, React Native, Rust, Python, Unity, and ESP32 embedded devices, while server-side APIs cover Node.js, Go, Ruby, Java, Python, Rust, PHP, and .NET. The Agents framework enables building AI-powered voice and video applications — real-time speech-to-text, LLM-driven conversations, and computer vision pipelines — running as server-side participants in any room. Egress records sessions to S3-compatible storage or streams to RTMP endpoints, while Ingress pulls external feeds from OBS via RTMP, WHIP, or SRT into LiveKit rooms. The SIP bridge connects traditional telephony to WebRTC rooms for hybrid conferencing. JWT-based authentication, webhook notifications, room-level moderation APIs, and selective subscription give operators granular control. Deploy as a single binary for development, Docker Compose for production single-node, or Kubernetes with the official Helm chart for distributed multi-region clusters using Redis for state coordination. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.

With over 16,500 GitHub stars and a track record powering connected vehicle fleets, smart city sensor networks, and industrial IoT deployments, EMQX is the MQTT messaging platform engineered to handle 100 million concurrent device connections in a single cluster while processing millions of messages per second with sub-millisecond latency. The protocol stack supports MQTT 5.0, 3.1.1, and 3.1 with full QoS 0/1/2 support, shared subscriptions, retained messages, and will messages, plus MQTT over QUIC for faster connection setup, reduced head-of-line blocking, and seamless connection migration on mobile networks. The gateway framework extends connectivity to MQTT-SN, CoAP, LwM2M, STOMP, and ExProto for bridging legacy industrial protocols. The SQL-based rule engine processes and transforms messages in real time with over 50 pre-built integrations including Kafka, PostgreSQL, MySQL, MongoDB, InfluxDB, TimescaleDB, ClickHouse, Redis, AWS Kinesis, GCP Pub/Sub, and Azure Event Hubs. The visual Flow Designer creates data processing pipelines without code. Built on Erlang/OTP with a masterless distributed architecture using Mria for state replication, the cluster separates Core nodes for data consistency and Replicant nodes for client-handling workloads. Authentication supports username/password, JWT, PSK, X.509 certificates, and LDAP with configurable ACL rules. The built-in dashboard provides real-time monitoring of connections, subscriptions, topics, message rates, and cluster health. Deployment runs via Docker, Kubernetes with the EMQX Operator, or native packages. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. BSL 1.1 licensed.

Why rent your messaging from a corporate walled garden when Tinode runs WhatsApp-style chats, groups, channels, and calls on a server you control? Teams get one-on-one and group chats that stay in sync across web, Android, and iOS, with typing indicators, delivery and read receipts, presence, replies, forwarding, editing, pinned messages, and notes to self. Communities broadcast through read-only channels with an unlimited number of subscribers, and granular permissions decide who can read, write, or invite on each topic. Support desks welcome anonymous visitors, mark staff and verified accounts with badges, and put chatbots to work with forms and templated replies. Messages take markdown-style formatting, inline images and videos, file attachments, and voice messages. One-to-one voice and video calls run peer to peer over WebRTC, using the TURN and STUN servers you configure. Administrators block unwanted contacts on the server, attach moderation plugins over gRPC, and script the rest with a command-line tool. Attachments can sit on local disk or Amazon S3, the database can be MySQL, PostgreSQL, or MongoDB, and sharded clustering with failover scales past one server. The clients offer light, dark, and system themes, custom chat wallpapers, and translations for more than a dozen languages. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

Convoy is an enterprise-grade webhooks gateway that manages both incoming and outgoing webhook traffic to guarantee reliable event delivery without exposing internal microservices to the public internet. Organizations deploy the platform at the edge to ingest events from message brokers such as Apache Kafka, RabbitMQ, and Google Cloud PubSub, or receive HTTP webhooks from third-party services directly. The gateway enforces delivery policies through configurable rate limiting per endpoint, circuit breaking during downstream outages, and automated retries using constant or exponential backoff with jitter. Developers can generate customer-facing webhook portals embedded via iframes, allowing end users to inspect delivery attempts, verify HMAC-SHA256 signatures, and manually replay failed events. Comprehensive security controls include static egress IP proxying to prevent server-side request forgery, automated rolling secret keys, and instant alerting via Slack or email when endpoints fail consecutively. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Elastic License 2.0 licensed.

One notify() call is all your product needs to reach users on push, email, SMS, chat, and webhooks, with NotifKit deciding how and when each message travels. List the channels in the order you prefer and NotifKit tries each in turn, so a failed push quietly becomes an SMS or an email instead of a lost message. Per-user preferences, consent, and quiet hours in each user's own timezone hold non-urgent sends until morning, while critical messages such as one-time passwords travel their own lane immediately. Templates, multi-step workflows that wait days or block on events, scheduling, throttling, and deduplication all run behind that single call, defined in TypeScript and kept in your repository. Delivery logs record every attempt, and the admin dashboard shows a live activity feed, queue depth per priority lane, workflow runs step by step, and a replayable dead-letter queue. Several products can share one deployment as separate projects with their own API keys, rate limits, and data, and any service can call the REST API without the TypeScript SDK. Ask an AI assistant why a password reset never arrived by connecting the built-in MCP server to Claude Code, Cursor, or another MCP client. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Powering notification delivery for thousands of organizations with over 39,000 GitHub stars, Novu is the open-source communication infrastructure that eliminates the need to build separate integrations for every messaging channel. The TypeScript-based platform provides a single API endpoint that routes notifications across In-App Inbox, Email via SendGrid, Mailgun, AWS SES, and Postmark, SMS through Twilio, Vonage, and Plivo, Push via Firebase Cloud Messaging, Expo, and APNS, and Chat through Slack, Discord, Microsoft Teams, and WhatsApp. The embeddable React Inbox component delivers real-time WebSocket-powered notifications with read/unread states, action buttons, and user-controlled preferences directly inside your application. The workflow engine orchestrates complex multi-channel delivery with conditional branching, time delays, digest batching to reduce notification fatigue, throttle controls, and per-step channel fallbacks. Novu Connect introduces Agent Communication Infrastructure enabling AI agents built with LangChain, Claude, or custom frameworks to hold threaded two-way conversations with humans across any supported channel through a single conversation model with identity resolution and credential management. The backend runs on Node.js with NestJS, MongoDB for notification storage, Redis with BullMQ for job queuing, and Socket.io for real-time delivery. Self-hosting deploys via Docker Compose with the dashboard accessible at port 4200. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Real-time alerts from your own infrastructure to your phone, with no Firebase, Pushover, or third-party push service in the path: Gotify is a simple, self-hosted notification server written in Go. The model is deliberately minimal: senders push messages with a single HTTP POST to the REST API, receivers subscribe over a WebSocket stream, and a clean React web UI manages the pieces. Senders are namespaced as "applications," each with its own token, so your backup script, Uptime Kuma, CI pipeline, and cron jobs each get an identity, an icon, and independently revocable credentials - centralized alerting from many services with per-source management. Messages carry a title, body, and priority level that maps to notification importance on the client. The official Android app (on both F-Droid and Google Play, notable for working entirely without Google Play Services) shows push notifications for new messages; the web UI itself supports Web Push in the browser; and gotify/cli pushes messages from shell scripts with one command. A server-side plugin system adds custom behavior, and the whole thing runs as a single small binary with SQLite by default - near-zero resource footprint. Because dozens of tools (and Apprise) speak Gotify natively, it slots in as the notification hub for an entire homelab or ops stack.

Used by over 80% of Fortune 100 companies including LinkedIn, Netflix, Uber, and Goldman Sachs, Apache Kafka processes trillions of messages per day as the world's most widely deployed distributed event streaming platform. Since version 4.0 released in March 2025, Kafka operates exclusively with KRaft consensus, replacing Apache ZooKeeper entirely with an internal Raft-based metadata quorum managed by controller nodes, reducing operational complexity and eliminating external coordination dependencies. Topics are organized as append-only partitioned commit logs with configurable replication factors across brokers, delivering network-limited throughput with end-to-end latencies as low as 2 milliseconds. Kafka Streams provides a client library for building stateful stream processing applications with exactly-once semantics, windowed aggregations, joins across streams and tables, and interactive queries against local state stores. Kafka Connect integrates with hundreds of systems including PostgreSQL, MySQL, Elasticsearch, Amazon S3, MongoDB, HDFS, and JMS through a standardized connector framework with distributed worker mode and automatic offset management. Share Groups introduced in version 4.2 deliver queue-style consumption semantics alongside traditional consumer groups, enabling Kafka to serve both pub-sub and point-to-point messaging patterns natively. The Schema Registry enforces Avro, Protobuf, and JSON Schema compatibility rules across producers and consumers, preventing schema evolution from breaking downstream applications. Tiered Storage offloads older log segments to object storage like S3 while maintaining transparent consumer access, dramatically reducing local broker storage costs for long-retention topics. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.