Unobtrusively detects form submissions made by spambots, and silently drops those submissions. The key word here is "unobtrusive" -- this is NOT a CAPTCHA. This is a transparent, modular implementation of the bot-catching techniques discussed by Ned Batchelder at http://nedbatchelder.com/text/stopbots.html.
Gemfile gem 'bot-away', '~> 1.0.3'
install gem install bot-away -v 1.0.3