When I was looking for something to Audit the network I manage I had a go with a few free tools. This came out on top and we are using it still!

Slow, Slow, Slow....
This tool is impossible to use in real environment!
:(

Spiceworks is an excellent program for network administrators to keep track of network devices, software, and anything else you can think of.
It's extremely customizable, and comes with built in support from your peers in the IT world.
It also comes with a fantastic help desk feature, that will allow your users to put in help tickets, which in turn help you keep track of problems you've had in the past, so you can be better equiped to resolve those problems in the future.
There are way too many features to put down here, you really should go to their website and check the program out for yourself.