Here's the Ruby client for Stomp, written by Brian McCallister, now maintained by Johan Sørensen:
Stomp is also available as a ruby gem:
gem install stomp
If you are working with Ruby on Rails then you really should check out ActiveMessaging more details on the Wiki.
ActiveMessaging (or a13g for short brings the power of Stomp to the Ruby on Rails world in a similar way ActiveRecord did for databases.