Rainpress
Rainpress is a free (MIT-style license) CSS compressor written in Ruby. It could be used either as a library or as a standalone executable. Rainpress doesn't apply common compression algorithms like gzip, it remove unecessary characters and replaces long attributes with an shorter equivalent.
History
For the Schoorbs we wanted to build releases packages and optimize all files, where a optimization made a significant increase. Already available CSS compressor were either only available via HTTP or not were less efficent.
Releases
Version 1.0 was lately released
Links