Free Downloadable Computer Games?

K Gingers, need your help! I need to download an awesome game for my laptop to play offline. I know I'll probably find one myself, but I'd love to hear all your suggestions!

MineCraft is very, very fun, I've heard, and if you need to find a server because your real life friends don't have one, Cake Lair has a server, but depends on if you like the people in it. I have Risk II, and it's addicting to play with friends or even just the computer. Plus, it goes much faster than the board game. You could get Dungeon Defenders for PC. It may have online, and I know a few Cake Lair people got that. Stripy plays a free online game called Roblox, which looks pretty fun.