Minetest

Minetest is a free and open-source game, created by Perttu Ahola. It is just like Minecraft but it can be freely played. The original author of Minetest simply described it as a "Minecraft clone".
In the default game of Minetest, Minetest Game (MTG for short), players explore a 3D world made from cubic blocks. Players may discover and extract raw materials, craft tools and items, and build structures and landscapes. Players can change the game settings to fight computer-controlled "mobs", as well as cooperate with or compete against other players in the same world. The game can be played with mods, which edits the gameplay.
As the game developed over the years, Minetest has been praised and is a popular game. Since November 2013, Minetest has been downloaded over 1.4 million times from GitHub, and the Android version of Minetest has over 500 thousand downloads on the Google Play store.
Gameplay
Minetest is set in a world full of blocks shaped like cubes. Gameplay is in the first-person camera for normal, but players also have the option for third-person camera. The game world is composed of in-game 3D objects, many of them are just simple cubes, commonly called nodes. Different in-game nodes (blocks) represent different materials, such as dirt, stone, ores, tree trunks, water, and lava. The core gameplay revolves around picking up and placing these objects, one node at a time. Nodes are arranged in a 3D grid, while players can move smoothly around the world. Players can mine blocks and then place them somewhere else, granting the permission to them to change (modify) the game world. Players can also craft a wide variety of hand-held tools to help them with the world change. Pickaxes allow players to dig rocky nodes, shovels speed up the digging of dirt and sand, water buckets allow to pick up water nodes, etc. A player controls a 3D character known as Sam, which is first-letter acronym for "Sam ain't Minecraft".
As players explore the world, new areas are officially generated by using a map seed randomly or choosed by the player. A new game puts the player in the center of a voxel cube 62 thousand blocks across, so the player can travel 31 thousand blocks in any direction like sideways, up, or down before reaching the invisible wall (the barrier) at the end of the world.
The world is divided into biomes ranging from deserts to jungles to snowfields; the terrain includes plains, mountains, forests, caves, and various lava and water bodies. The in-game time system follows a day and night cycle, and one full cycle lasts 20 real-time minutes just like Minecraft.
Minetest provides only two basic game mode options: Enable Damage and Creative Mode which affect how players interact with the world and use items. Creative Mode is meant to provide players with infinite resources, while toggling the damage setting decides whether the players can take damage from environmental hazards and other players.
Multiplayer
Minetest has a built-in client-server architecture, and can be played solo or multiplayer. A player starting a new game can choose between playing in a single-player mode, or hosting a server to which other Minetest players can connect.
Customizations
The full source code of Minetest, and all of its artistic assets such as textures and sounds, are distributed under a variety of free licenses, making it easier to create changed versions and derivatives. The base version of Minetest provides an interface for games and mods written in Lua. Games define the basic rules of the game world, and are a core feature of Minetest. Most games feature sandbox gameplay focused on construction, mining, and creativity. Mods are used to further customize different parts of gameplay, and are an permanent part of Minetest. Mods are server-side and work out of the box when playing on Internet servers, with no manual installation needed.