If you've ever looked at the relatively limited firewall settings on your internet router and wondered what it would be like to run and manage a proper enterprise-level firewall, here's something that may interest you.  (And conversely, if playing with corporate-grade IT isn't something that excites you, you may wish to stop reading at this point).

In the world of UTM (Unified Threat Management, otherwise perfectly sensibly known as simply "security"), Sophos is a well-known player.  Its UTM appliance is a self-contained computer that acts as a fully-featured firewall as well as managing the security of your network as a whole. It also includes features such as web site filtering, to stop the kids from accesing sites they shouldn't, and mail filtering to help prevent spam.

Although the full product costs many thousands of dollars, you can also get a home version completely free, which you download and install onto a spare PC.

It's the complete corporate version, but licenced only for home use and limited to a network of no more than 50 IP addresses.  Which should be plenty.

You will, as mentioned, need a spare PC for this.  Once you've downloaded the software from http://www.sophos.com/en-us/products/free-tools/sophos-utm-home-edition.... and burned it to a disc, and then installed it onto said spare computer, you'll have a ready-to-play UTM appliance complete with its own operating system.  

As mentioned, this is serious kit for serious fiddling, so don't expect to have it up and running in 10 minutes.  But if you're interested in such things, and have a spare PC (or a virtual machine), then give it a try.  There's lots of useful information on the Sophos web site to help you.