\_ IRCII should work for this one.
\_ 
\_ (text based)
\_ 
\_ Unless you talking about system messages then read 
\_ following man pages:
\_ 
\_ write
\_ mesg
\_ wall

Or the ever popular 

cat > /dev/tty12

YMMV on that.  The best was the early version of unix that had perms
on the ttys wide open.

cat long_ansi_graphic_file > /dev/luser-tty

echo "System going down now...exit!' > /dev/lamer-tty

Of course, my favorite exit inducer I pulled on some guys playing
xtrek (yes, it was still called that then) on machines *I* needed....
They obviously didn't know about xhost, so I gradually twisted their
mouse sensitivity up.  Firing accuracy was the first to go, but they
didn't get the hint...thought it was just lag.  I think they finally
bailed at 500/1 which affected basic navigation.  Their opponents
didn't have navigation or firing problems somehow.  :-) Although it
comes to mind that I had to twist the mouse back down so that they
could get to the logout menu.  Heh.  BOFH with non op status.

David