Holla – An Open Source Group Chat Application
Holla is an open source group chat application where you can create channels, invite friends to those channels, chat and share files.
It has a totally Ajaxed interface on every level (messaging, uploading files, etc.).
A nice feature is that the file uploads can be done via drag'n drops and every user in the chat can see the upload progress bar.
Holla uses Node.js for the real-time chat and falls back to Comet and Flash Sockets if WebSockets is not supported.
The application is actually a "sample resource" for the upcoming book of the author -which on asynchronous interfaces- and has a demo too.