MyBB Community Forums

I want to use something that's provably based in php?

there is a chat irc mod available for mybb...

check the mods database

The pJIRC mod is quite good. For one it allows users who don't have an IRC client installed to chat on your forum. Also since it's using IRC (presumably on a network such as Dalnet or Efnet, etc), it doesn't stress your server as a Flash- or AJAX-based chat would. Also since it's on IRC, any IRC junkies on your site can use their own IRC client to connect to the chat, and IRC is so much cooler than any flash-based chat anyway since you can be entertained by other people's disasters