PRK Firmware is the world's first keyboard firmware framework in Ruby. You can write not only your own "keymap" in Ruby but also additional behavior by features of Ruby like open class system and Proc object.
Plus, your keyboard itself interprets a Ruby script on the fly. Essentially, your keyboard can become Ruby.
The ultimate goal is certainly not a small one --- let's make Ruby comparable to projects such as MicroPython, CircuitPython or Lua in terms of viability as a scripting language for microcontrollers.