10
FlashChat, at $5, is great if your users need an easy to use chat interface. It is great looking and easy to use for the users. This pays for future upgrades, as well, which are ongoing.
Installation was a breeze, and with the XOOPS integration instructions, it will use the XOOPS login. It also automatically uses the "Who's Online" block to indicate that people are in chat.
The only down sides are, it costs $5 and your users need to install Flash.