Act vs Bun

act is an open-source command-line tool that runs GitHub Actions workflows locally using Docker containers. It reads workflow files from .github/workflows/ and executes them with environment variables and filesystem configurations matching GitHub's hosted runners. The tool enables fast local feedback on workflow changes without requiring commits and pushes to a remote repository.

Bun is a fast all-in-one JavaScript runtime, bundler, transpiler, and package manager built with Zig and JavaScriptCore. It aims to be a drop-in replacement for Node.js with significantly faster startup and execution times.