Bun is an all-in-one JavaScript/TypeScript toolkit shipped as a single native executable: a JavaScriptCore-powered runtime, an npm-compatible package manager, a bundler/transpiler, and a Jest-compatible test runner. The code confirms this: src/bun_bin is the CLI entry point; src/install is a full package manager with its own binary lockfile format, workspaces, and isolated/hoisted installers; src/bundler, src/css, and src/js_parser implement JS/TS/JSX/CSS/HTML bundling and transpilation; src/jsc and src/runtime implement the runtime with Web platform APIs, an HTTP server (Bun.serve), WebSocket support, SQL clients, and a Node.js compatibility layer (src/js/node, src/js/internal). It also embeds a React Compiler port for automatic memoization and a shell interpreter (Bun.shell). The repo is fundamentally an application, not a data/research project; the only research-flavored content is compiler-semantics fixture corpus and benchmark scripts.
workerd is Cloudflare's JavaScript/Wasm server runtime powering the Cloudflare Workers platform. It implements a nanoservices architecture where all services are deployed to every machine, using a capability-based security model for isolation. The runtime executes serverless Workers in response to HTTP requests, queues, scheduled events, and other triggers, providing APIs for HTTP, storage (KV, Durable Objects, R2), websockets, and more. The core is implemented in Rust and C++ with bindings for JavaScript/TypeScript and Python via Pyodide. Key entry points include the `workerd` CLI binary (built via Bazel) and the Rust `workerd_cli::main()` function. The system processes requests by routing them to Worker isolates, which execute user scripts and can access bindings for subrequests, storage, and other services. It includes extensive compatibility layers for Node.js APIs and Web standards, along with a comprehensive test suite validating spec compliance and implementation correctness.
LLRT is a low-latency JavaScript runtime built in Rust around the QuickJS engine, designed primarily for AWS Lambda serverless workloads. The actual code confirms it is both a CLI runtime and a Lambda custom runtime: the `llrt` binary enters Lambda mode when `AWS_LAMBDA_RUNTIME_API` is present, and `runtime_client.rs` implements the full invoke/handler/response loop. It also provides `llrt compile` to emit QuickJS bytecode and self-contained executables, and `llrt test` to run a built-in Jest-compatible test runner. The runtime reimplements a broad surface of Node.js and Web APIs in Rust: `fs`, `net`, `http`, `crypto`/WebCrypto, `fetch`, `stream`/Web Streams, `events`, `timers`, `buffer`, `url`, `os`, `path`, `temporal`, `zlib`, `child_process`, `dgram`, and `intl`.