mandrill-api-ruby
It is a mirror for an official Mandrill API gem. For some reason the gem is currenly hosted at https://bitbucket.org/mailchimp/mandrill-api-ruby which is not so rubyist-friendly as github.
How To Use
All info you can find at the official RTFM page.
Credits
Send all your love to Mandrill API maintainers and commiters, not to me <3