Tagger: a library for extracting relevant tags from text documents
github.com
github.com
I believe it's pretty rough (and nearly all of the commits are "Misc. changes") but still. It's a port of some similar work in Python.
Ultimately I wish Ruby and Python would have sex and their offspring be compatible with both so that I can use the best of both worlds ;-)
Maybe they'll go out and one thing will lead to another.