A couple of nice projects I can think of are DragonRuby [1] - a 2d engine that uses SDL under the hood and mruby for its game logic. I created this [2] game jam entry in under two weeks of part time effort (has a few bugs but works)
[3] Sonic Pi - Music creation tool that uses ruby for instruction
The mistake that most folks make. They start out using RoR and think that’s Ruby.
That’s probably why Ruby will always remain a “web” language and won’t be taken _seriously_ in other areas.