Real-time command history sharing between interactive shells

[Andrew Pantyukhin]

I want to be able to define groups of interactive
shells (preferably even across different users)
so they have one single shared command history.
Any command executed in one of them should be
available through all history mechanisms in the
other ones.

I imagine some ways to do it in tcsh. I'm sure
many users would like this kind of functionality,
maybe some of them have already implemented it?

Thanks!