TypingIndicator is a tiny addon that shows you a small typing indicator (duh) when someone else who also has the addon types in guild, raid or whisper.
I have not even tested it with RealID, or even multiple chat frames. Maybe it works, maybe not.
To be clear, both the sender (typer) AND reciever (you) need to have this addon for you to see -anything-.
I wrote this because when I talk to people ingame it's really annoying when you have discussions and you don't know when you can type, or when you would actually be interrupting the other person. So it allows me to be less rude by limiting the times I actually interrupt them.
The addon has no config except /typi to move the indicator.
The indicator has a tooltip which lists if more than one person is typing, and it colors according to chat colors (green for guild, pink for whisper, etc, or whatever you have it set to).