Gin

Godot Engine is a full game engine for 2D, 3D, mobile, desktop, web, and consoles, completely free with no revenue share or per-seat licensing. It's a web framework: you define routes, attach handlers, add middleware for things like logging and auth, and it handles the HTTP plumbing.

MIT license. Gin is to Go what Express is to Node.js, the default answer when someone asks "which framework?" It's fast (built on httprouter), has a clean API, and the documentation is solid. You can go from zero to a working API in 20 minutes.

Everything is free. No paid tier, no commercial version, no cloud offering. It's a library you import into your Go project.

The catch: Gin is showing its age. The Go ecosystem has moved toward lighter frameworks like Echo and Chi, or even just the standard library's net/http with Go 1.22's improved routing. Gin adds convenience but also adds a dependency, and in Go culture, fewer dependencies is better. If you're starting a new project today, look at Hono (for the edge) or the standard library first. Gin is fine, battle-tested, and everywhere, but it's not the only answer anymore.