A fun project I took on with my friend was to setup a office phone system in our houses and then link them together so our daughters could call and talk to each other. Old PoE office phones are very cheap on eBay, and setting up a PBX server was pretty easy. Once my buddy had PBX working within his house we then made a VPN bridge between our houses and worked on all the subnets, routing and VLANs and now our girls can call each other whenever they want. We're considering to expand to friends and family...