Bun

Cal.com is a scheduling tool you can self-host: booking pages, calendar sync, team scheduling, payments, and workflows, all without giving Calendly your data. Runtime, bundler, test runner, package manager. One install, one tool. It's written in Zig and JavaScriptCore (Safari's engine) instead of V8, and the speed difference is real.

Installing packages is noticeably faster than npm or pnpm. The runtime starts faster than Node. The bundler is faster than esbuild in most benchmarks. The test runner is Jest-compatible but runs parallel by default.

Everything is free. No paid tier, no cloud offering. The license situation is technically listed as 'Other' but Bun uses MIT for the core runtime. You can use it commercially. Solo to large teams: free across the board. Drop it into any JS/TS project. It's Node-compatible enough that most packages work without changes.

The catch: 'Node-compatible' isn't 'Node-identical.' Some npm packages that depend on native Node APIs or specific V8 behaviors will break. The ecosystem is still catching up; CI environments, hosting platforms, and tooling don't always support Bun natively yet. If you're on a team with established Node infrastructure, migration has real costs. For new projects, it's a no-brainer to try.