An (abandoned) experiment w/ dragonruby
I bought dragonruby to check it out and got fairly far before I realized there were a lot of features that were missing (notably, a good REPL, 1-1 compat with a standard Ruby version, and debugging), and that the engine itself still required more baking before it would really be a "usable" 2d game engine.
One of the great things about Ruby is the ecosystem, and there's just too many gems that don't work at all - partially DR is it's own Ruby interpreter strapped on top of LLVM w/ some special bindings to GPL2.
There are better choices at this point, as much as I would like to use Ruby in a game jam. Hopefully the engine matures!