Tatsumaki, my tiny Perl port of Tornado using Plack and AnyEvent originally started as a proof of concept to test and demonstrate PSGI's streaming interface but its chat app using a simple long-poll Comet got a lot of attentions from people:
Audrey Tang used the MessageQueue and comet interface to build multi-person SocialCalc, Daisuke Maki packaged the chat app, gugod is building an iPhone IRC client and jshirley is doing some interesting to stream content with YUI.
Actually, by "tiny port" I mean Tatsumaki does most of the things Tornado does, but in a very limited but simple way: simple embedded Perl templates, non-blocking I/O for everything including built-in HTTP clients, long-poll Comet ready MessageQueue API, simple server side push (aka firehose) and Digg's multipart XHR push as a Comet replacement. Yes, it is really simple but exciting :)
I really didn't want to increase the number of modules/applications i maintain but now it has proven very useful when last night I wrote a new PubSubHubbub hub Subfeedr using Tatsumaki, Plack, AnyEvent and Redis in 3 hours: it's a polling PuSH proxy and everything works in the single process in the event loop non-blockingly (so nice).
So anyway, it's now on CPAN as well as on github , which makes it a little harder for me to change APIs and what not, but no worries, everything is undocumented, so you still have to peek at the code to do what you want to do :)