Ruby2JS is a Ruby-to-JavaScript transpiler with a modular filter architecture. It converts Ruby source code into JavaScript by parsing Ruby AST (via Parser gem or Prism) and applying a pipeline of filters that transform Ruby idioms into JS equivalents. The project includes a self-hosting capability (transpiles itself to JS), a Rails-like micro-framework called 'juntos' for building full-stack JS apps, and build tool plugins for Vite, esbuild, Rollup, and Webpack. It supports multiple output targets (ESM, CJS, JSX, React, Lit, Stimulus, etc.) and framework-specific filters for Rails, Phlex, Vue, Svelte, Astro, and more. The architecture is well-structured with clear separation between parsing, filtering, conversion, and serialization. The codebase is actively maintained with extensive test coverage and a monorepo structure for npm packages.