Free Network Usage Monitoring Tools

[CommodoreS]

Please could anyone recommend any good free network monitoring usage tools?

 

There seem to be quite a few which monitor the network and tell you of problems. I am just after something which reports when a machine has been switched on\off and when a user has logged in and off, perhaps also reporting a username to get an idea of how much the system is being used and who is using it the most.

 

Can anyone recommend any free (or extremely cheap) tools that would do this please?