Chatting about mathematics (with real-time LaTeX rendering)

Solution 1:

LaTeX plugin in Pidgin:

http://sourceforge.net/projects/pidgin-latex/

This screenshot is taken from http://sourceforge.net/projects/pidgin-latex/screenshots/124729

Solution 2:

Mathim - online chat with the possibility to use of LaTeX syntax (the first result that google returned for latex online chat or latex online chat math)

http://mathim.com

Screenshot from my short experiment with this tool:

Mathim was also discussed here:
http://www.physicsforums.com/showthread.php?t=193510
http://www.physicsforums.com/showthread.php?t=196699

It is possible to copy the text of session (simply by selecting it) and put it into a TeX file.

Solution 3:

The web interface of hack.chat renders LaTeX, and there are some pre-made rooms for math, physics, etc. It's also open source and can be installed on your own server if needed.