ruby-growl is a platform-independent Ruby library for sending Growl notifications.
Growl (http://growl.info) is a really cool notification system for Mac OS X.
You can get the full scoop on ruby-growl here:
http://segment7.net/projects/ruby/growl/
You can download ruby-growl as a gem:
http://segment7.net/projects/ruby/growl/ruby-growl-1.0.0.gem
Or as a .tgz:
http://segment7.net/projects/ruby/growl/ruby-growl-1.0.0.tgz