esbuild
JavaScript/TypeScript bundler written in Go. 10–100× faster than Webpack. Evan Wallace (Figma CTO), 2020. Base for Vite, tsup, Tauri bundling.
Bundles 10 MB JS in <1 sec. Pitch: one man + Go = faster than the whole Webpack team with JavaScript. Stable since 0.16 but hasn't taken 1.0 (deliberately, "stable enough"). Vite uses esbuild in dev mode + Rollup in build (Rollup gives better tree-shaking). Competitors: Rollup (more optimizing), SWC (Rust, Next.js default), Bun build (Zig), Lightning CSS (for the CSS part). Rolldown (Vite team, Rust) is the future default.