shugo/textbringer: An Emacs-like text editor written in Ruby https://github.com/shugo/textbringer
Combines #Emacs and #Ruby -- a great idea :)
It's fun to see and learn from an implementation like this. There are books on the topic, on how you need a window to render to, a buffer to represent the whole content, and this project uses gap buffers as recommended. Nice.