Buy Minecraft, which apparently is on sale for $14.99. It's not quite as fun when all your friends have the official version and get to play together while you're stuck with an - *ahem* - unofficial version.
For zero monies you & your friends could run VoxeLibre which has better performance characteristics. Microsoft doesn’t deserve your money or your user data, but I am sure VoxeLibre or Minetest wouldn’t mind a donation.
They are more than complete/polished with multiplatform support, with healthy modding communites, & better performance since they aren’t built on Java. In the past your money went to the developers—now it goes to megacorp Microsoft with little done in terms of maintenance.
On the topic of games, Stick Fight The Game is $5 on steam and I got it while drinking with a few friends. It was the most fun I've had in years. I also hop on randomly when I get a chance and it's just as fun with random people.