Free
Socket.IO
Open SourceAPI Protocols · Backend
Reliable bidirectional realtime communication over WebSockets.
websocketrealtimejavascript
Browse the complete directory — use filters to narrow down.
API Protocols · Backend
Reliable bidirectional realtime communication over WebSockets.
Programming Languages
Official Solidity language site for Ethereum smart contracts.
Frameworks · Frontend
Declarative UI library with fine-grained reactivity and no VDOM.
Frameworks · Backend
The Java ecosystem for building production-grade applications.
Frameworks · Backend
Opinionated Spring setup for standalone production-ready apps.
SQL Tools
Popular open-source JavaScript library to format SQL in your apps.
ORMs · Backend
The Python SQL toolkit and ORM standard.
Relational · Database
Self-contained, serverless, embedded SQL database engine.
Penetration Testing · Security
Open-source penetration testing tool that automates SQL injection detection and exploitation.
Compression & Optimization · Image & Media
Google's browser image compressor with advanced codecs (WebP, AVIF).
Agent & LLM Frameworks · AI for Developers
The classic browser UI for Stable Diffusion image generation.
Terminals & Shells · Development Environment
Fast, customizable shell prompt written in Rust, works with any shell.
PDF Tools · PDF & Documents
Self-hosted PDF toolbox with 50+ operations, locally run.
Build & Lint · Frontend
Industry-standard workshop for building, testing and documenting UI components.
Ecosystem · CSS Tools
CSS-in-JS library for React with scoped, dynamic styles.
Ecosystem · CSS Tools
The linter that keeps your CSS clean and consistent.
Frameworks · Frontend
Compiler-based UI framework with no virtual DOM and great DX.
Compression & Optimization · Image & Media
Node.js tool and library for optimizing SVG vector files.
Compression & Optimization · Image & Media
Browser GUI for SVGO, optimizing SVG files with previews.
Build & Lint · Frontend
Rust-based TypeScript/JavaScript compiler used by Next.js and friends.
Programming Languages
Official Swift.org open-source project site with docs and downloads.
State & Forms · Frontend
React Hooks for data fetching with caching and revalidation.
Frameworks · Backend
Mature PHP framework and set of reusable components.
References · Documentation & Learning
The most-starred system design study guide — scalable architectures, trade-offs and exercises, free and open source.