If you are looking for a web based multi user chat script then here is one which you can try for free which is named Candy. Candy is a real-time multi-user chatting script which is easy for a developer to configure. It comes with well-documented and Built for XMPP (Jabber).
- Focused on real-time multi-user chatting
- Easy to configure, easy to run, easy to use
- Highly customizable
- Built for Jabber (XMPP), using famous technologies
- Used and approved in a productive environment with up to 400 concurrent users
- Works with all major web browsers including IE7