Hookbox is a Comet server and message queue that tightly integrates with your existing web application via web hooks and a REST interface.

how to build realtime web applications using node.js, V8 and WebSockets.

# uses script tags for communication, but can detect when a script isn't loaded (this is non-trivial to implement across browsers)
# works across domains as long as you control the domains
# works on IE 6, IE 7, IE 8, FF X, Safari, Chrome and Opera
# small (80 lines of code) with no dependencies

Get XMPP - BOSH working with Ejabberd, Firefox and Strophe

Q: How well does the Nginx HTTP push module perform with 10 000 concurrent clients? (Ye olde C10k problem).

A: Very well. About 7 kB per client and practically zero CPU load.