Internet filtering

Hi all,

I wonder if there are any software (Preferably free) that I can use to track what others are doing on their computers and filter the internet?

The host computer will be connected to the Internet by ethernet, while the other computers will be connected to the host computer by wireless (as the host will be running a AP with the built-in wifi card).

And then the host computer can tell me where other users have been to on the Internet.

Thanks all in adv!

EDIT:
The software will NOT be installed on the user's respective computers, but on the host computer.
Setup is similar to how organisations and schools track their staff and student internet usage