Minetest is an infinite-world block sandbox game and a game engine, inspired by InfiniMiner, Minecraft and the like.
It is designed to be simple, stable, and portable. It is lightweight enough to run on fairly old hardware.
Minetest allows you to walk around, dig and build in an infinite voxel world, and craft stuff from raw materials; it includes a simplistic Modding API that supports many kinds of additions and modifications to the game. There is multiplayer support via servers hosted by other users and support for multiple languages translated by the users within the community.