Yarn
JavaScript package manager. Facebook + Google + Exponent, October 2016. Was faster than npm v3 → pushed npm to improve. Yarn 2 ("Berry", 2020) changed architecture (Plug'n'Play).
v1 (Classic) — still most used, parallel install + lockfile + workspaces. v2+ (Berry) — Plug'n'Play eliminates node_modules (controversial). Competitor: pnpm (symlink-based, most disk-efficient), Bun (fastest 2024). Facebook still uses Yarn internally. Trivia: pnpm + Yarn Berry both hated npm v7+'s "auto-install peer deps" behavior.