Minetest
Minetest is a free and open-source sandbox video game and game creation system developed by a team of volunteers, with significant contributions from the community. The first publicly available version was Minetest 0.0.1, created by Perttu Ahola, and released on the Web in November 2010. "Minetest" is programmed in C++ using the Irrlicht Engine, and is available for Linux-based systems, FreeBSD, Microsoft Windows, MacOS, and Android. "Minetest" provides an API for users to create their own games and mods written in Lua. In "Minetest", players explore a blocky, procedurally-generated 3D world with seemingly infinite terrain, and  may discover and extract raw materials, craft tools and items, and build structures and landscapes. Depending on game mode and mods present, players can fight computer-controlled "mobs", as well as cooperate with or compete against other players in the same world. The game mechanics of "Minetest" are similar to those of the 2009 game "Minecraft", though the original author stopped just short of describing it as a ""Minecraft" clone". Over a decade of active development "Minetest" has garnered critical acclaim and gained in popularity; 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. "Minetest" has also been used in school education to teach abstract thinking and as an interactive visualization tool. "Minetest" is free software since November 29, 2010, allowing users to study and modify both the source code and the included art. Gameplay. "Minetest" is a voxel sandbox video game that has no specific goals to accomplish, allowing players a large amount of freedom in choosing how to play the game. Gameplay is in the first-person perspective by default, but players have the option for third-person  perspective. The game world is composed of voxels: 3D objects, many of them simple cubes, commonly called "nodes". Different voxels represent various 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" (or "dig") blocks and then "place" (or "build") them elsewhere, enabling them to modify the game world. Players can also craft a wide variety of hand-held tools to aid them with the  world modification. Pick axes allow 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 a recursive acronym for "Sam ain't "Minecraft"". The game world is very large and appears to be infinite for many practical purposes. As players explore the world, new areas are procedurally generated, using a map seed specified by the player. A new game puts the player in the center of a voxel cube 62 thousand nodes across, so the player can  travel 31 thousand nodes in any direction (sideways, up, or down) before reaching the invisible wall at the end of the world. Storing the entire voxel array of that size would require hundreds of terabytes of memory, but the game sidesteps this requirement by splitting the world data into smaller 16x16x16 sections called "map blocks" that are only created or loaded when players are nearby. The world is divided into biomes ranging from deserts to jungles to snowfields; the terrain includes plains, mountains, forests, caves, and various lava/water bodies. The in-game time system follows a day and night  cycle, and one full cycle lasts 20 real-time minutes. "Minetest" provides two basic game mode options: "Enable Damage" and "Creative Mode" which affect how players interact with the world and use items. Creative Mode is intended to provide players with infinite resources, while toggling the damage setting determines whether the players are able to take damage from environmental hazards and other players. Multiplayer. "Minetest" implements a client-server architecture, and can be played solo or with other people over the Internet. A player starting a new game can choose between playing in a single-player mode, or hosting a  server to which other "Minetest" clients can connect. For hosted games, there is an option to announce them at the public server list. Alternatively, a player can browse the public server list and connect to one of the Internet servers. Many "Minetest" servers are run by volunteers who are not affiliated with the "Minetest" project, and feature wildly different rules, options, and modifications, with game modes that can be described as cooperative voxel art, player-versus-player survival, capture the flag, etc. 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 modified 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 various aspects of gameplay, and are an inherent part of "Minetest". "Mods" are server-side and work out of the box when playing on Internet servers, with no manual installation required. Players can also download  texture packs to change the appearance of nodes. Games. Developers refer to "Minetest" as an engine rather than a "game" because almost every aspect of gameplay is implemented within so-called "games" written in Lua. Since version 5.0.0, the main menu of the "Minetest" engine allows users to browse and install "games" from a curated list. "Minetest" is shipped with two "games": Minetest Game implementing a feature-rich sandbox, and Development Test implementing a minimal sandbox useful for debugging. Minetest Game implements a simple and peaceful game with no goals and no built-in computer enemies. It features over 200  node types and a variety of digging tools, trees, flowers, ores, biomes, and caves. Mods. There are over 1000 free and open-source mods available at Minetest forums. Since version 5.0.0, "Minetest" features a built-in content picker, allowing users to browse a curated list of add-ons and install mods and texture packs with a single click. Mods can be used to add node types, tools, monsters, player skins, and alter many aspects of the gameplay. Both the forums and the in-game browser exclude non-free or closed source software as a matter of policy. Development. Minetest was  originally released in November 2010 under a proprietary license. Shortly afterwards the license was changed to the GPL-2.0-or-later license. By agreement among major contributors, in June 2012 the project license was to be changed to LGPL-2.1-or-later, though at the time small parts still remained under the GPL-2.0-or-later license. In September 2013, the transition was complete. While LGPL-2.1-or-later remains the main license for the "Minetest" engine, other free and open-source licenses are used for various other parts of the latest release. Perttu Ahola was the only developer working on the project for  about six months, until Ciaran Gultnieks started making code contributions in May 2011. The roster of contributors grew and changed over the years. As of July 2020, there are 9 active core developers and 15 active contributors. "Core developer" is considered primarily a position of trust, and they are the ones deciding what is merged into the upstream repositories, and do not necessarily contribute the most by volume. Project participants do not have set roles, but rather keep their activity within their respective areas of expertise. Perttu Ahola's role morphed over the years: whereas initially it was engine development , now it is mostly Web-hosting and administration, assigning core developer, moderator, and other roles to people, as well as being the final word in cases where other developers are unable to render a decision. Usage in education. "Minetest" has been used in educational environments to teach subjects such as mathematics, programming, and earth sciences. Its advantages over similar commercial titles include zero cost, allowing for massive deployments in a classroom or a research setting. Also, "Minetest"'s graphics engine, while not fully optimized for the most recent hardware, performs very well on a wide range of low-cost, low -end hardware. Reception. Opensource.com listed "Minetest" at #1 in its "Best open source games of 2015", stating that it is maybe "the most complete alternative to "Minecraft"", and noted its expansibility, stating that it contains a user-friendly API for creating mods in Lua. PC Magazine listed "Minetest" among "The best Sandbox Creation Games for "Minecraft" Fans".