Do you know about some tools which can be used for online chat about mathematics? In particular, I am interested in software which would be able to render LaTeX formulas. (Since LaTeX is probably the fastest possibility to type mathematics.)
Have you tried some of them? What are their advantages and drawbacks?
NOTE 1: In this question I am asking only about solutions how to type mathematics in chat, not about possibility to use video and sound. (For the purposes of this question, assume that only keyboard, mouse and display are plugged to your computer.)
NOTE 2: I will post some possibilities I am aware of in the answers. But I would be grateful if someone who tried these applications could expand these answers a little more.