Invoicerr nails the exact billing sequence freelancers actually use: draft a quote, send it to the client, collect a legally-binding electronic signature via a secure browser link, convert the approved quote into an invoice, and generate a branded PDF — no DocuSign account, no external signing service, no enterprise complexity. The React frontend with NestJS backend uses Prisma ORM with your choice of SQLite for instant local setup or PostgreSQL for production workloads. Quotes and invoices are first-class objects with independent status tracking — unread, sent, viewed, signed for quotes; paid for invoices — not a single form with a label swap. The e-signature system generates secure-token signing links that clients open in their browser to review and sign documents without needing any account or external service. PDF generation renders quotes, invoices, and receipts with your company logo, name, VAT number, colors, and custom email templates so documents reflect your brand identity rather than the software's defaults. Authentication supports JWT tokens or OIDC providers stored in cookies. The REST API backend enables future integrations with mobile and desktop clients. A plugin system with community-made features and outgoing webhooks extends functionality without forking core code. International-friendly with customizable currencies. Deploy with Docker Compose using the prebuilt image from GitHub Container Registry. 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.

Trusted by Mistral AI, PayPal, Groq, and Synthesia with over 10,300 GitHub stars and Y Combinator backing, Lago is the open-source billing engine that handles usage-based, subscription-based, and hybrid pricing models through a single API-first platform — replacing the need to build custom billing logic or depend on opaque SaaS pricing infrastructure. Real-time event ingestion via ClickHouse processes billable events with deduplication and multiple aggregation methods including count, sum, unique count, max, and weighted sum, while graduated pricing tiers, package-based billing, and percentage-based fees model any pricing strategy from simple subscriptions to complex marketplace commission structures. Automated invoice generation calculates charges according to configurable billing cycles with grace periods, proration for mid-cycle changes, and credit note issuance for refunds and adjustments. Prepaid credits enable pay-in-advance models where customers purchase credit blocks and draw down as usage accumulates, while entitlements tie feature access directly to billing plans for automated provisioning and de-provisioning. Payment orchestration integrates natively with Stripe, Adyen, and GoCardless with automatic retry logic, dunning workflows for failed payments, and multi-gateway routing. Revenue analytics provide cross-stream visibility into MRR, usage trends, churn, and revenue drivers through dedicated API endpoints. The customer portal embeds into your application for self-service invoice access and usage monitoring. 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.

Kill Bill handles the complete subscription billing lifecycle from plan definition through invoice generation to payment collection across any gateway, with 15 years of Fortune 500 production use and 5,600+ GitHub stars behind it. Plans, trials, add-ons, and pricing tiers live in a versioned XML catalog that propagates changes without code deploys. The multi-phase subscription engine manages trial periods, promotional discounts, evergreen billing, usage-based metering, and hybrid pricing models with automatic proration on plan upgrades and downgrades. Automated invoice generation calculates charges, applies credits and adjustments, and triggers payment collection through pluggable gateways including Stripe, Adyen, Braintree, PayPal, and CyberSource. The Java plugin framework extends every billing domain with custom logic for tax calculation via Avalara AvaTax or Vertex, fraud detection through Accertify or Feedzai, and ERP integration without modifying the core. The Kaui admin dashboard gives finance and operations teams account management, subscription controls, invoice views, payment configuration, billing timeline visualization, MRR tracking, advanced search, and full audit history with object-level change tracking. Multi-tenancy isolates billing data across thousands of brands with tenant-specific catalogs, payment configs, and RBAC policies. REST APIs expose every operation with webhook notifications for downstream integration. Deploys via Docker Compose on MySQL or PostgreSQL. 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.

Flexprice is a developer-first billing platform built specifically for AI-native and SaaS companies that need usage-based, credit-based, and hybrid pricing models without building custom billing infrastructure. The metering engine ingests millions of usage events in real time through HTTP APIs or SDK calls, supporting sum, count, unique count, latest value, and multiplier aggregation strategies across custom event schemas like API calls, token counts, compute minutes, and GPU time. Credit management handles prepaid wallets with promotional grants, rollover caps, auto top-ups, and priority-based credit application during invoice generation. The pricing engine supports per-unit, tiered, volume, package, and flat-rate models with per-customer overrides, committed minimums, and enterprise contract terms. Feature entitlements enforce boolean toggles, metered usage limits, and configuration values per plan, enabling applications to gate functionality through simple API checks. Automated invoicing calculates charges from real-time usage data with proration for mid-cycle upgrades and downgrades, generating detailed line items linked to tracked consumption. The architecture separates event ingestion through Kafka from billing computation via Temporal workflow orchestration, allowing each layer to scale independently with ClickHouse handling high-performance usage aggregation. Stripe Connect integration processes payments and manages customer payment methods. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPLv3 licensed.

With nearly 10,000 GitHub stars and over a decade of development since 2013, Invoice Ninja is the most complete source-available invoicing platform for freelancers and small businesses — combining professional invoicing, online payments, expense tracking, and project management in a single self-hosted application. The Laravel API backend powers a React web portal and Flutter native applications for Windows, macOS, Linux, iOS, and Android, delivering a consistent experience across every device. Create professional invoices and quotes with real-time PDF preview, product libraries, custom templates, and automatic tax calculations. Clients receive branded emails and access their dedicated portal at your custom domain to view documents, approve quotes with e-signatures, and pay with one click via Stripe, PayPal, Square, GoCardless, Authorize.net, Braintree, or Mollie. Recurring invoices with auto-billing charge saved payment methods on schedule — weekly, monthly, or annually — with automatic reminders and late fee calculations. The built-in project management suite includes Kanban boards for task organization, billable time tracking with start/stop timers, and vendor expense management with receipt attachments. Bank account synchronization via Yodlee or GoCardless automatically imports transactions for reconciliation. E-invoicing with PEPPOL network integration supports electronic invoicing standards for European and government compliance. Reports cover invoices, expenses, profit and loss, tax summaries, and aged receivables. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Elastic License v2.

Used by Tailwind Labs and recognized as an official GitHub funding partner, Polar is the open-source billing infrastructure that lets developers ship production-ready monetization in hours instead of weeks. Meter tokens, API calls, agent runs, GPU seconds, and storage with event-level precision, then compose usage billing with subscriptions, seats, credits, trials, and discounts into whatever pricing model your product requires. As Merchant of Record, Polar handles sales tax, VAT, chargebacks, receipts, and regulatory compliance across all supported countries so you receive clean payouts without building tax infrastructure. Integrate via the full REST API with official SDKs for JavaScript, Python, PHP, and Go, plus framework adapters for Next.js, Astro, Remix, SvelteKit, and Laravel enabling checkout integration in minutes. Automatically deliver benefits upon purchase including GitHub repository access, Discord roles, license keys, file downloads, and meter credits through configurable automation rules. The built-in customer portal provides subscription management, payment method updates, invoice history, and benefit access with full white-label branding. Monitor revenue, costs, and margins through real-time analytics dashboards showing the unit economics every AI startup needs to scale. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache License 2.0 licensed.

SolidInvoice ships a complete billing platform as a single FrankenPHP binary — no separate PHP installation, no web server configuration, just one executable that delivers quote-to-invoice conversion, automated recurring billing, Stripe and PayPal payment processing, multi-currency precision arithmetic, and eight render-ready PDF templates out of the box. Maintained since 2012 across 63 releases with 30 contributors, the Symfony 7 and PHP 8.4 backend provides quote creation with one-click conversion to invoices, recurring billing with configurable frequency schedules, and online payment processing through Payum supporting Stripe, PayPal, and additional gateways. Multi-currency support uses real Money objects for precision arithmetic, while multi-tax support handles invoice-level and line-item tax rates with automatic calculation. Client management stores contacts, multiple addresses with map integration, credit balances, and complete quote and invoice history per client. The redesigned Tabler-based UI features a dashboard with hero statistics, ChartJS revenue trend visualization, attention-required alerts for overdue and draft invoices, quick actions, and a recent activity timeline. A RESTful API enables integrations with external systems. Multi-channel notifications deliver alerts via email, SMS, and webhooks. Google OAuth and two-factor authentication secure access. Grid export and full company data export support backup and migration. Deploy using Docker, Homebrew, the standalone FrankenPHP binary, or from source. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Meteroid delivers the billing infrastructure that SaaS companies need when Stripe Billing gets too rigid and building in-house gets too expensive. The Rust backend ingests usage events via REST API or Kafka with deduplication by event ID and customer ID, storing time-series data in ClickHouse for sub-second aggregation queries across billions of events. Billable metrics transform raw events — API calls, compute time, tokens, storage, transactions — into accurate charges using configurable aggregation functions, dimensions, and filters without pre-aggregation. The plan builder supports any pricing structure: flat rate, per-unit, tiered graduated, tiered volume, package, and hybrid combinations with multiple price components per plan. Versioned plans enable pricing changes without affecting existing subscribers through grandfathering, while experiments let you A/B test pricing with controlled rollouts. Subscription management handles the full lifecycle — creation, upgrades, downgrades, mid-cycle proration, scheduled changes, and cancellation with configurable grace periods. The TypeScript frontend provides a complete web dashboard for managing customers, plans, subscriptions, invoices, and revenue analytics with MRR tracking, churn analysis, and cohort insights. Automated invoice generation handles complex scenarios including usage-based line items, credits, discounts, and tax calculations with PDF rendering. Stripe Connect integration enables payment collection directly through the platform. 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.

Create an invoice, share a secure link, get paid — that's the entire workflow, no client portals or account registrations required. Invio distills billing into its absolute minimum viable surface while still producing legally compliant EU electronic invoices in Factur-X/ZUGFeRD 2.2 BASIC, UBL 2.1, and Italian FatturaPA formats, all embedded as XML attachments inside WeasyPrint-rendered PDFs. The Deno 2 backend uses Hono v4 for HTTP routing with SQLite persistence, while the SvelteKit 2 frontend styled with Tailwind CSS v4 and DaisyUI v5 delivers a responsive interface that stays out of your way. The team access system includes a permission matrix, TOTP-based two-factor authentication, and OIDC integration with configurable auto-provisioning — drop it into existing identity infrastructure without manual user management. Preset products let you build invoices from reusable catalog items. A change history log tracks every modification for audit purposes. Rate limiting protects the API behind reverse proxies. The entire stack ships as a single multi-stage Docker image containing Deno, Bun, Node, WeasyPrint, and all required font packages — zero external service dependencies beyond the container itself. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Unlicense licensed.

InvoicePlane manages the complete freelance and small-business billing cycle — draft quotes, convert them to invoices, automate recurring charges, collect payments through Stripe and PayPal, and generate EU-compliant eInvoice XML for automated processing by accounting systems. Deployed over 100,000 times across 193 countries, the PHP 8.2+ application on CodeIgniter 3 with MySQL or MariaDB handles everything from first estimate to final receipt. EU-compliant eInvoice generation creates machine-readable XML invoices meeting European Union standards since version 1.6.2. Recurring invoices automate periodic billing with configurable controls that pause generation when previous invoices remain unpaid. Online payment integration lets clients pay directly through Stripe, PayPal with Advanced Credit Cards, and Venmo support. The CRM-like client management module stores contact details, notes, custom fields, and complete transaction history per client. Product and task management modules let you build line-item invoices from reusable product catalogs and project tasks. Customizable PDF templates powered by mPDF support branded invoice layouts with QR codes, while email delivery via PHPMailer handles automated sending with configurable SMTP. A guest portal gives clients read-only access to view and pay their outstanding invoices and quotes. Financial reporting tracks revenue, outstanding balances, and payment history. The multi-language interface supports community translations, and multi-currency handles international invoicing. Deploy via Docker Compose with automatic database migrations. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Small MSPs waste thousands of dollars annually on overlapping subscriptions for documentation, ticketing, and billing tools that don't talk to each other. ITFlow replaces that fragmented stack with a unified platform where client contacts, locations, vendors, computer assets, software licenses, domains, SSL certificates, passwords, and documents all live under one roof. The AES-encrypted password vault stores credentials with organized access controls, and domain plus SSL certificate tracking generates automated renewal alerts before expiration disrupts client services. Ticketing supports creation, prioritization, assignment, and SLA tracking, with a client portal where customers submit tickets, view invoices, approve quotes, and access their own documentation independently. The accounting module covers the full lifecycle: quotes, recurring billing, expense tracking, Stripe payment processing, and financial dashboards showing revenue and outstanding balances at a glance. AI integration through Ollama, LocalAI, or ChatGPT accelerates documentation writing and ticket responses directly within the interface. The modular architecture lets you enable only what you need, sidestepping the bloat of enterprise PSA platforms designed for organizations ten times your size. With stable releases since 2025 and zero per-user licensing, ITFlow removes the escalating costs that make commercial PSA tools unsustainable for growing teams. The PHP application deploys with MariaDB and Nginx, ready for production in minutes.

Named after the Bosnian word for invoice (račun) with a raccoon twist, Rachoon provides a clean self-hosted invoicing platform that handles the complete billing cycle from quotation to payment reconciliation without touching a third-party SaaS subscription. The Nuxt.js frontend serves a dashboard that surfaces revenue totals, pending balances, overdue items, and client statistics at a glance, while the AdonisJS backend manages all business logic against a PostgreSQL 16 database with TypeScript throughout the full stack. Invoice templates use Nunjucks with full HTML and CSS control—including conditional logic, loops, and custom formatting—so the rendered PDFs actually match your design intent. This is possible because Rachoon delegates PDF generation to Gotenberg, which renders invoices through headless Chrome rather than a restricted drawing API, producing output that faithfully preserves complex layouts, web fonts, and CSS grid. Client records stay organized and searchable, each linked to their invoice and quotation history with payment status tracking across pending, paid, and overdue states. Multi-currency billing with flexible tax configuration supports international operations, and all data remains on your own infrastructure. The monorepo is managed by Turborepo with a CI pipeline covering linting, PostgreSQL integration tests, build verification, and multi-platform Docker image creation for both amd64 and arm64 architectures. 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.