Minecraft is a 8 bit indie game with over 5 million players.
The game is a giant sandbox, free build, pvp, survival game.
There are several gamemodes, aswell as homegrown ones (RPG for example)
PVP - Fairly self explanatory, players can build houses, and towns, and go to war with each other or simply kill each other, players can destroy each other towns etc.
Survival - Players Rush to gather supplies and build shelters before nightfall to protect them from the creatures of the night (Zombies, creepers, spiders, skeletons etc.) (can also be combined with PVP mode for survival pvp mode)
Free build - Commands such as /give (item) (amount) so you can construct art and buildings.
RPG - Build your houses, create your own town, interact with others (everything RPG is)
The game is currently in alpha and is one time buy charge of 15$.
The requirements are fairly minimal, all you really need is a computer newer then 1999.
Minecraft Fanmade Trailer