These are just a few little things from a collection I wrote long ago in
college on an IBM RS/6000 running AIX.

afk.c        "Locks" your terminal with a password
apb.c        Sends your message to everyone logged on with mesg on
call.c       Sends your message to the specified person logged on
whoison.c    Lists everyone logged on (like who, but faster)

I may toss some other intersting stuff in here later on.