 The current release 1.1.5 is no longer able to install in Ruby versions higher than 1.9.2 which is recommended for Rails 3, the fix is to use the much older 1.2.0-pre2 release of Mongrel which isn't stable.A new and maintained server, called Thin, uses the Mongrel parser.The Mongrel parser has also been forked by Unicorn and by Puma.