Dead links are magically transformed into live links! Rack::Linkify is very generous in what it considers a link; it will turn www.google.com, www.google.com, and just plain google.com into a link.
Rack::Linkify can also turn text that looks like @this into a twitter link.
URLs only:
use Rack::Linkify
Enable Twitter links, too:
use Rack::Linkify, :twitter => true