Options for comet servers for ruby/ruby on rails?

What frameworks exist for developing comet applications using Ruby on Rails?

Ideally, whatever options I find should make my life easy when choosing a hosting provider

(I'd rather have something that works with existing web servers, rather than something that requires an exotic开发者_运维技巧 comet-enabled web server)

Thank you!

Have a look at Rainbows! - It's based on Unicorn but meant for "sleepy apps and slow clients".