Pipey's Flash Chat is a web-based chat system based on Macromedia Flash and Active Server Pages (ASP) technologies. It overcomes the problems of many HTML-based chats by using interactive Flash movies as the user-interface. And what's more, it is very easy to customise. Here's a list of the main features:

Configurable background graphics.
Multiple Rooms.
Password-protected (private) rooms.
'Skins' - allow the user to choose from a selection of backgrounds.
Chat operators - special users who can kick or ban other users from the chat.
Multi-language support - change the interface text to any language.
Private messages.
'Mood icons'.
Full Flash source to modify as you please (registered version only).
Users can print out a transcript of their chat session.

The chat is free for non-commercial use. A licence to use the chat on a commercial site (any site operated by or for a profit-making organisation) currently costs $9.99 per site, and that includes full source files for the Flash interface.