The following are commonly used social commands:
users - Simple list of who is online.
who - List of who is online and from where.
w - Verbose information on who is on and what they're doing.
finger - Get more information about someone.
chfn - Change your finger information.

ttys - What are ttys and what do they mean to you.

write - Start a simple one way communications with someone.
talk - Start a full screen two way communications with someone.
ytalk - Like talk, but up to 7 way communications.
mesg - Enable or disable requests for communication.