Workling is a plugin that allows you handle complex or long running processes outside of the normal Rails request/response cycle. You can configure how it to use various runners; currently, there is a Spawn runner and a Starling runner. This kind of sidesteps the issue of not knowing which Asynchronous code running method is the best for your rails app. Potentially, you could swap in any mechanism you like.
See the GitHub wiki page for the most up to date version and usage information.
Author: Play/Type GmbH
Installation:
ruby script/plugin install git://github.com/purzelrakete/workling.git