Reminds me of my sysadmin days when I was trying to learn shell scripting and would lookup man pages of random binaries in /usr/bin. Before we could bring down a box for nightly maintenance/backup, we would send a shutdown broadcast notice like:

banner "Shutdown"|wall; banner "in 5 mins"|wall

I found out "write" command and setup a hacky little one-to-one chat script - it was terrible and geeky but I really liked it.

I'm probably forgetting some more obscure commands that I enjoyed :)

PS: forgot to mention that when I told my boss about the "write" based scripts, he gloated that he had setup a quiz program which supported multiple participants using named pipes. Awesome guy :)