Rubidium is a Ruby cheminformatics scripting environment. Previously, a problem was reported with the RubyForge gem repository that prevented the simple installation of the Rubidium gem. After filing a bug report, the problem was resolved.
The problem, which led to a 404 being issued when trying to install the gem from the remote RubyGems repository, was a variant of a known RubyForge issue.
You can now install Rubidium like this:
$ jruby -S gem install rbtk
Installation takes a few minutes due to the large size of the included Chemistry Development Kit jarfile.