who

The who command displays information about the currently connected users,
including how long they have been connected, how long they have been idle,
and whether or not they are set zoned (away). The zoned flag is specified 
by an asterisk (*) by someone's name.

You can give who any number of arguments, separated by spaces:
An argument of the form "+" or "-" followed by "byon", "byidle", "byname",
or "bydoing" sorts the players listed, by their on-time, idle-time, player
name, or @doing. A + sorts in ascending order, and a - in descending. The
default is "+byon" unless you have set your own default (see "help whomode").
Any player's name given as an argument will be listed (whether the player
is online or offline).
Specifying "#channel" will list all members of that channel who are online.

If no players or channels are listed, the who command will list all online
players.

The who command also  displays how long the ifMUD system has been up and
running since it was last restarted.

Usage:
who
who Spatch
who schep inky markm
who +byon
who #monkey
who -byidle #perl