There's a freeware game called Infiniminer that was released a few days ago, and it was a lot of fun last night. It's a FPM (First Person Miner), like Dwarf Fortress without the carp, in 3D, and first-person. You mine ore to build blocks, jump pads, dynamite, and other things. The object is to either find a certain amount of gold and jewels before the opposing team, or simply building neat structures deep in the earth (while trying not to fall into the lava). It's way more fun than it should be.
As noted, it's freeware, and easiest to play using Hamachi. When you download it, make sure you also download the XNA Runtime or it will instantly crash when you run it (a lot of people including myself skipped that step). Once you get it, make sure you choose Edit Player Configuration in the start menu item to give yourself a name (if you're making a server, which is shit-easy to do, likewise increase the ore from 10% to like 80% if you want to do a lot of building). Then just pop the Hamachi IP into Direct Connect and tada, minin' fun.
Edity: I decided to add a couple screenshots of gameplay. Here I've dug down a bit into the earth and found some lava:
Stupid lava. I decided to build a bridge over it, a ladder to the surface, and used some blue force field blocks next to the ladder to make it harder for the pesky blue team to use it - blue players will fall through it while red players will be able to walk over it:
Special thanks to Ralewyn for finding this for us.
Quick note, current server is MisterSyn's (see IRC for details), but his version is 1.3 while the latest is 1.4. You can get 1.3 here. NEVERMIND HE IS NOW 1.4ING NOW 1.5 GET IT NOW DO IT