This easy to install, simple to handle, cross-browser compatible chat system comes with its own socket server.

If you have a modern browser with frame support and JavaScript enabled, it makes use of these technologies; if you have an older browser, have JavaScript disabled, or even a text browser, you can still chat using this script.
In contrary to many other PHP/MySQL webchats, this script can (but must not) be run using a non-forking socketserver to handle all message transport.