Rainbows

Rainbows! is an HTTP server for sleepy Rack applications. It is based on Unicorn, but designed to handle applications that expect long request/response times and/or slow clients.
For Rack applications not heavily bound by slow external network dependencies, consider Unicorn instead as it simpler and easier to debug.
If you’re on a small system, or write extremely tight and reliable code and don’t want multiple worker processes, check out Zbatery, too. Zbatery can use all the crazy network concurrency options of Rainbows! in a single worker process.

http://rainbows.rubyforge.org/