You can use others if you like. I have used Crystal before, pretty quickly realized that it was never going to catch up with Ruby and the compile step isn't really all that much of an advantage. The few scripts that I want speed for, I just use mruby. Embed Ruby in C, runs super fast. Don't get all the cool Ruby libs or runtime reflection. But a way better tradeoff.
https://github.com/ruby/rbs
You can use others if you like. I have used Crystal before, pretty quickly realized that it was never going to catch up with Ruby and the compile step isn't really all that much of an advantage. The few scripts that I want speed for, I just use mruby. Embed Ruby in C, runs super fast. Don't get all the cool Ruby libs or runtime reflection. But a way better tradeoff.
https://mruby.org/