InvoicePrinter is a Ruby library for generating PDF invoices, with additional CLI and HTTP server interfaces. It takes structured invoice data (as Ruby objects or JSON) and generates formatted PDF documents using the Prawn library. The system consists of three main components: the core library for PDF generation, a command-line executable for direct use, and a server executable providing a HTTP API. The architecture shows good separation of concerns with distinct modules for data models, PDF rendering, font handling, and server interface.
Kimai is a self-hosted, open-source time-tracking application built with PHP 8.3+ and Symfony 6/7. It provides a full-featured web interface and REST API for recording timesheets, managing projects/customers/activities, generating invoices, exporting data (PDF, XLSX, CSV, HTML), and producing reports. The architecture follows a classic Symfony monolith with Doctrine ORM, Twig templating, and Webpack Encore for frontend assets. It supports multi-user, multi-timezone, multi-language, LDAP/SAML authentication, two-factor authentication, and a plugin system via tagged services and compiler passes. The codebase is heavily event-driven, with over 70 domain events and subscribers, and includes a rich set of dashboard widgets, custom form types, and validation constraints. The repository is actively maintained with frequent commits, extensive test coverage (PHPUnit), and continuous integration pipelines.
EasyInvoicePDF is a free, open-source, browser-based invoice generator that creates PDF invoices with live preview, no sign-up required, and no ads. Built with Next.js (App Router), React 19, TypeScript, Tailwind CSS, and shadcn/ui, it runs entirely client-side for the public editor—invoice data stays in localStorage and is never uploaded to a server. The application supports 10 languages, 120+ currencies, two PDF templates (default and Stripe-inspired), QR codes, multi-page PDFs, and shareable compressed URLs. A private server-side API (Bearer token + Upstash rate-limited) handles monthly recurring invoice generation via Trigger.dev cron, uploading PDFs to Google Drive, emailing via Resend, and sending Telegram notifications. The codebase also includes extensive SEO landing pages, a changelog, a founder page, and comprehensive testing (Vitest unit tests, Playwright e2e with PDF screenshot baselines). Architecture: The app uses two root layouts—unprefixed English-only routes (/) and locale-prefixed routes (/[locale]) for i18n via next-intl. The main invoice form is a large client component with react-hook-form and Zod validation, debounced autosave, and template/language switching. PDF rendering uses @react-pdf/renderer on the client for live preview and on the server for automation. External dependencies include Upstash Redis (rate limiting, queue), Resend (email), Google Drive (archive), Telegram (notifications), Sentry (error tracking), Umami (analytics), and Trigger.dev (scheduled tasks). The repository also contains a rich ecosystem of agent skills (Vercel React best practices, composition patterns, SEO audit, etc.) used in development workflows. Key data flows: User fills form → state stored in localStorage and optionally shared via compressed URL → PDF preview rendered client-side via @react-pdf/renderer → download or share. For monthly automation: Trigger.dev cron triggers server-side PDF generation → upload to Google Drive → email via Resend → Telegram notification. The backend API also supports a preview endpoint for sample PDFs and a Telegram webhook for on-demand generation.
Invoice Ninja is a full-featured open-source invoicing and billing platform designed for small to medium businesses. It handles the complete lifecycle of invoices, quotes, credits, purchase orders, payments, and expenses. The system supports multi-tenant SaaS and self-hosted deployments with per-company database isolation, and integrates with over 20 payment gateways (Stripe, PayPal, Mollie, GoCardless, etc.). It provides client and vendor portals for self-service, along with extensive reporting, CSV export, and e-invoicing capabilities (Peppol, Verifactu, France e-reporting). The application follows a monolithic MVC architecture built on a custom PHP framework (Illuminate) similar to Laravel. It uses an event-driven architecture with domain events and listeners for side effects (email, webhooks, activity logging). Background jobs are queued for async processing. The frontend uses Blade templates, Livewire components, and a separate React app for some admin panels. The API is RESTful with OpenAPI documentation. Key entry points are HTTP controllers under app/Http/Controllers, with request validation classes. Core data flows involve creating entities through factories, persisting via repositories, and triggering events that listeners handle. Payment flows go through abstract payment drivers that encapsulate gateway-specific logic. The system also includes extensive reporting, CSV export, and e-invoicing (Peppol, Verifactu, France e-reporting). External dependencies include a relational database (MySQL/PostgreSQL), Redis for caching and queues, Elasticsearch for search, and various third-party APIs for payment processing, tax calculation (ZipTax), bank integration (Nordigen, Yodlee), email delivery (Mailgun, Postmark, Brevo), and e-invoicing gateways (Storecove, Qvalia).
IDURAR is a free, open-source ERP and CRM application built on the MERN stack (MongoDB, Express.js, React.js, Node.js) with Ant Design and Redux. It provides modules for invoice management, payment processing, quote generation, customer relationship management, inventory tracking, and financial reporting. The system features multi-language support (44 languages), PDF generation for business documents, role-based access control, and a responsive user interface. The architecture separates concerns with a RESTful API backend and a modular frontend utilizing React, Redux for state management, and Ant Design for UI components.