Something I've been working on
I've been working on this project for approximately 2 months now; NetBlocker. It's basically a network/classroom management tool which allows administrators/staff to block internet access to groups of computers (such as rooms) and to individual accounts, it also makes use of Active Directory to easily allow you to import the computer groups based on your already existing OUs. You also have the option to modify groups, create your own groups, create exempt lists etc. When blocking users/groups, you can either permanently block them, or set a time at which they'll automatically be unblocked. The software will be free of charge, and is aimed as schools/organisations who can't afford to buy the well-known network/classroom management tools, it's not aimed at replacing what already exists. I've also tried to make sure that it's as easy as possible to setup, deploy and remove from computers.
This is only a brief post describing the software, I will provide more information nearer to the release (hopefully within a month).
Screenshot of the administration tool (there's also a separate tool which can be deployed to staff, which is a basic version of the administration tool):
If you have any suggestions/queries post them here, or send me a pm :)