TalkerApp launched
talkerapp.tumblr.com
talkerapp.tumblr.com
I built a little toy app that used BOSH and ejabberd to do chats - upside is you get all the extensibility of XMPP and the downside is that you have to deal with all the extensibility of XMPP. :)
We use Orbited for comet. The backend chat server is custom and based on RabbitMQ. See our protocol on https://talker.tenderapp.com/faqs/api/talker-protocol
(this comes from someone who contributes to and writes plugins for a campfire bot:
http://github.com/joshwand/campfire-bot
)
Hm....quit tempting me!
Talker also has a free version (4 concurrent users) https://talkerapp.com/signup/free
DabbleDB is another app that does this: http://dabbledb.com/help/guides/jsapi/