An open-source video game, or simply an open-source game, is a video game whose source code is open-source. They are often freely distributable and sometimes cross-platform compatible. Many are included in Linux distributions as a result.Open source games which are free software and contain exclusively free content are called free games. Most free games are open-source, but not all open-source games are free software; some open-source games contain proprietary non-free content.BackgroundIn general, open-source games are developed by small groups of people in their free time, with profit not being the main focus. Almost all open-source games are volunteer-run projects, and as such, developers of free games are often hobbyists and enthusiasts. The consequence of this is that open-source games often take longer to mature, are less common and often lack the quality of commercial titles. One of the challenges to building high-quality content for games is it often requires expensive tools like 3D modeller or a toolset for level design.Some of the open-source game projects are based on formerly proprietary games, whose source code was released as open-source software, while the game content (such as graphics, audio and levels) may or may not be under a free license. Examples include Warzone 2100 (a real-time strategy game) and Micropolis (a city-building simulator based on the SimCity source code). Advantage of such continuation projects is that these games are already "complete" as graphic and audio content is available, and therefore the open-source authors can focus on porting, fixing bugs or modding the games.