author of GridFlow?, MetaRuby?, RubyX11.
MetaRuby? explores the relationship between class and interface. It proposes container classes that mimic the original ones (of Ruby) with added flexibility. MetaRuby? was also supposed to contain homoiconic tools, to process Ruby code as data structures, but that's been postponed to another decade.
RubyX11 is the smallest implementation of an X11 protocol library. It is written in a declarative style. A small fraction of the code is actually doing anything protocol-wise, and the rest is mostly a direct translation/distillation of the spec. This implementation is even shorter than the spec itself.
GridFlow? is a clone of the APL Array Programming Language, but specialized in realtime video processing in the context of visual dataflow programming environments (such as MAX and such, that were originally designed for interactive music).
All those three are open-source projects; at the time of this writing (2003.04) only GridFlow? is actively maintained.