This project is no longer actively developed, but it looks like an excellent resource for anyone who is interested in compilers. Ruby is an easy language to grok, so it should make for (relatively) easy reading!
Rhizome is a paedagogical just-in-time compiler (JIT) for Ruby, implemented in pure Ruby. It’s not really designed to be used. It’s designed to show you how JITs work and why perhaps a JIT for Ruby should be written in Ruby. It’s also designed to try to go beyond the trivial aspects of a simple template compiler that introductions to JITs often show - instead it has a proper intermediate representation (IR) and shows how more advanced parts of compilers such as lowering and schedulers work, that people don’t usually cover.