Have been using it in production for years for small projects. But also have a current, larger project in it that is going well. A few years ago I built a high throughput (20k shortens/s) link shortener for work, in Go. I later rewrote the main path in Crystal to test it for performance. It was a bit faster than the Go version (22k/s) on the same infrastructure… but running on a single core! We did not finish/ ship it, but it was revealing.