http://frug.github.com/AJAX-Chat/
(Let me know if you want to see the chat. Ours is private, so I'll have to set up authentication) Not to mention it's highly extensible.
No one has to reinvent chatting IRC works perfectly js
That's true, but my school blocks all non HTTP(S) or FTP ports, and ergo, prevents me from connection to IRC. All web based clients appear to be blocked, so it's possible this could provide an alternative for those who are unable to access IRC.
Port 53 is restricted to the approved DNS servers. The block is DNS based. Proxies rarely work, and tend to be extremely slow on said network. Only solutions I've found are a vpn or TOR. Regardless, I tend to center on BitcoinTalk or my friend's chat at school.