Teams that cannot send messages through someone else's cloud run Mattermost - the open-core, self-hosted alternative to Slack. It provides public and private channels, threaded discussions, unlimited search history, file sharing with previews, one-to-one audio calls, and screen sharing, with desktop clients for Windows, macOS, and Linux plus iOS and Android apps. Messages support full Markdown, which suits engineering conversations with code blocks and logs. Playbooks turn repeatable processes such as incident response and release management into checklist-driven workflows with automated triggers and retrospectives. Integration is a core strength: prebuilt connectors for GitHub, GitLab, Jira, ServiceNow, and PagerDuty, plus webhooks, slash commands, bots, a REST API, and a plugin marketplace with 700+ entries - together making it a working surface for ChatOps rather than just a chat room. Playbooks add keyword and event triggers, task assignment, status broadcasting, and post-incident retrospectives, so operational knowledge is not trapped in individuals' heads. The server is a single Go binary backed by PostgreSQL, with React clients, released monthly under MIT license and deployable fully air-gapped - which is why governments and defense organizations run it inside closed networks, and why the same control applies to any team with confidentiality requirements. The compiled Team Edition is free for unlimited users with no message history cutoff, so costs stay flat as the team grows.

Your team's group chat could have a colleague who has read every email, ticket, and document, remembers all of it, and answers in seconds; MindRoom puts AI agents like that into your chat rooms as full participants. Each agent is a real user on the open Matrix protocol, so you talk to it in MindRoom Chat on web or mobile, in any other Matrix client, or through bridges in Slack, Telegram, WhatsApp, and Discord. Give every agent its own model: a local model for private rooms, a frontier model for hard coding problems, and switch per room or thread whenever the work changes. Agents connect to more than 100 tools, including Gmail, calendars, GitHub, Google Drive, Home Assistant, and any MCP server, and they search your own documents and knowledge bases for answers with sources. Memory persists across conversations and platforms, so an agent remembers people, preferences, and project context months later and can turn repeated work into reusable skills. Before an agent sends an email or runs a command, an approval card shows exactly what will happen; you tap once to allow it, and sandboxed workers keep executed code away from your credentials. Schedule morning briefings, silent inbox checks, and recurring digests in plain language, or wake an agent from any other system with a single HTTP request. 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.

Used by the Rust language community, NASA, Dropbox, and thousands of organizations worldwide with over 25,600 GitHub stars and 1,500+ contributors, Zulip is the only modern team chat app designed from the ground up for both real-time and asynchronous communication through its unique topic-based threading model where every message belongs to a named topic within a channel. This eliminates the context collapse of linear chat by letting teams follow specific conversations without scrolling through unrelated messages, resume threads days later without losing context, and catch up on missed discussions at per-topic granularity. Server 12.0 introduced end-to-end encryption for mobile push notifications, AI-powered search ranking, channel folders for workspace organization, and expanded video conferencing with Jitsi, BigBlueButton, and Zoom integration. Over 100 native integrations connect GitHub, GitLab, Jira, Sentry, PagerDuty, Travis CI, Redmine, dbt, Nextcloud, and n8n with bidirectional notifications, while LLM-driven agents access web-public channels via a standard llms.txt interface. Full-text search covers unlimited message history across all plans, code blocks render with syntax highlighting for 250+ languages, and LaTeX math expressions display inline. The REST API with typed Python and JavaScript SDKs enables custom bots, webhook integrations, and programmatic administration. Import tools migrate entire workspaces from Slack, Microsoft Teams, Mattermost, and Rocket.Chat. 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.

Think of it as a team messaging platform where every feature beyond core chat is a plugin you can install or remove, inspired by VS Code's extension model but applied to real-time communication. The Moleculer microservice backend scales horizontally across nodes while Socket.io delivers instant message synchronization with text, images, files, mentions, reactions, and rich Markdown formatting. Available plugins provide LiveKit video conferencing, collaborative drawing boards, task management panels, end-to-end encryption, custom themes, and third-party push notification reception without touching core code. Groups use a two-level space system with customizable panel layouts arranged through drag-and-drop, while role-based access control enforces fine-grained permissions across the organization. The Open Platform exposes OAuth for single sign-on across connected applications and a Bot API enabling bidirectional message processing between Tailchat and external services via HTTP requests. Multi-platform clients cover web, Electron desktop with screenshot capabilities, and mobile apps with native push. Docker Compose deployment bundles MongoDB for persistence, Redis for caching and transport, and MinIO for S3-compatible file storage. Deploy on RepoCloud with a dedicated VPS for persistent team infrastructure under the Apache 2.0 license.

Matrix's flagship client, built by the protocol's creators: Element brings the decentralized open standard for real-time communication to web, desktop, iOS, and Android. Paired with a Matrix homeserver, it delivers Slack-quality team messaging where you own every message, file, encryption key, and byte of metadata. End-to-end encryption is on by default, built on Olm and Megolm - the Double Ratchet algorithm family Signal popularized, extended for large-room scalability and publicly audited by NCC Group. Messages encrypt per-device with cross-signed device verification, so even a compromised server yields nothing readable. Federation is the defining capability: like email, users on different homeservers converse seamlessly, and 30+ bridges connect Matrix rooms to Slack, Discord, WhatsApp, and Telegram, so moving to sovereign infrastructure doesn't sever contact with anyone. Rooms support threads, reactions, file sharing, and voice and video calls via Element Call. The result is digital sovereignty chosen by governments and enterprises across Europe: your data sits on your server in your jurisdiction, portable to any other Matrix host because the protocol is an open standard. Apache-2.0 licensed, with no per-user fees at any scale.

Dobase replaces the scattered pile of team subscriptions with one self-hosted workspace where mail, kanban boards, documents, chat, to-do lists, files, a calendar, and video rooms live side by side. Install only the tools your team needs, and share each one with exactly the collaborators you choose; a board for the whole company and a private todo list can sit in the same window. Several people can type in the same document at once, watching each other's colored cursors while the text merges cleanly, and presence faces in the sidebar show who is inside every tool right now. Open tools arrange themselves as tiles in a wide window, so chat can sit next to the board it discusses and the calendar under the mail you are answering. Pressing Cmd+K searches cards, todos, documents, files, chat, events, and mail in one motion, and nearly everything also works from the keyboard alone. Mail threads conversations and lets you accept calendar invites from the message, files get public links guarded by a password and an expiry, and the calendar syncs with CalDAV services or runs on its own. Video rooms with screen sharing join the same workspace, mentions and notifications follow you, and an email digest catches up anyone who was away. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

With nearly 5,000 GitHub stars and a Hacker News launch that garnered 147 points, Colanode delivers the first genuinely local-first alternative to both Slack and Notion in a single self-hosted workspace — writing every operation to a client-side SQLite database before syncing to your server, so teams work at full speed offline, on planes, or through intermittent connections without ever losing a draft. The real-time chat system provides channels and direct messages with instant delivery via WebSocket, while the rich text editor offers Notion-style block-based pages for documents, wikis, meeting notes, and knowledge bases with headings, code blocks, embeds, and nested hierarchies. Customizable databases organize structured data with custom fields and three dynamic views — table for spreadsheet-style browsing, kanban for visual workflow boards, and calendar for time-based planning. Conflict-free Replicated Data Types powered by Yjs handle concurrent editing across pages and database records: multiple users modify the same document simultaneously and the system merges changes automatically without manual conflict resolution. File management supports upload, sharing, and organization within workspaces using pluggable storage backends including local filesystem, S3-compatible services, Google Cloud Storage, and Azure Blob Storage with TUS resumable uploads for large files. The server runs Fastify with Zod validation on Node.js 20+, persists to PostgreSQL with pgvector extension, uses Redis for event broadcasting, and deploys via a single Docker image. 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.

Most team chat keeps people in one app and AI agents in another; Octo Server is the backend that puts both in the same conversation. It powers the OCTO workplace, where Lobsters, the platform's OpenClaw-powered AI agents, sit in channels as first-class participants that read context, run tool calls, and report back alongside their human teammates. Every request flows through one pipeline: token and cookie authentication, organisation-aware role checks and per-channel permissions, business logic that can start or resume an agent session, then fan-out through WuKongIM for real-time delivery. Channels support threaded subspaces, shared files, and a GROUP.md document that stores the group's standing context where the whole team can edit it. The smart summary service reads busy channels and produces structured digests, so catching up means reading one brief instead of hundreds of messages. External bridges connect conversations to GitHub, WeCom, Feishu, and Loop through adapters, and webhooks push group events to your own systems. The official one-command deployment runs the server with the web client, admin console, task service, WuKongIM, MySQL, Redis, and MinIO behind nginx, scaling as one backend that every client speaks to. 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.

Your team chat can be one executable on your own server: Campfire Rust runs rooms, direct messages, attachments, and search as a single binary that replaces the whole Ruby, Puma, Redis, Resque, and Thruster stack. Create rooms with access controls for projects, departments, or a private board discussion, and keep direct messages beside them for quick questions. File attachments arrive with previews, mentions pull the right person into a thread, and search finds the decision someone made months ago. Web Push notifications reach browsers and phones, so a quiet room still finds its people when it matters. Chatbots connect through a simple HTTP API for sending and receiving messages and attachments, which makes Campfire a home for build alerts, deploy notices, and support pings. Existing Campfire installs upgrade in place because the Rust binary reads the same SQLite database, storage layout, and signed cookies, with no data migration and no mass sign-out. Automatic TLS with Let's Encrypt certificates, HTTP/2, and Action Cable-compatible WebSockets are built in, and the whole system works on air-gapped networks that never touch the internet. Run it as your primary chat, as a backup for the day a hosted service goes down, or as a walled garden for executives and events. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.