HttpBL is IP-filtering middleware for Rails 2.3+ and other Rack-based applications. It resolves information about each request's source IP address from the Http:BL service at http://projecthoneypot.org, and denies access to clients whose IP addresses are associated with suspicious behavior like impolite crawling, comment-spamming and email-harvesting.
Rack
gem install httpbl
See: Here.
Brandon Palmen
Official releases can be found at Rubyforge
Development releases are hosted on GitHub in zip or tar formats.
You can also clone the project with Git by running:
$ git clone git://github.com/bpalmen/httpbl