whowatch is a console application that lets you monitor what different users are doing on the Linux operating system in a given moment, it works in real time.

First install it

sudo aptitude install whowatch

Now to run it just enter whowath in the command line, some screen like this will appear.

If you press ENTER while on a given username you will see the info about the programs that user is running.

Like this:

As you can see below you may see some command that lets you get more info about the user, and the programs being run by him.

If you go to "menu" by pressing F9 from the main menu, you will also be able among other things to send kill, HUB or TERM signals to the processes running, you can also use the keyboard for that with

^K for Kill
^U for HUP
^T for TERM

A pretty useful tool for admins