MUDs, also known as multi-user dimensions or dungeons, are text-based online gaming environments that have been around since the 1980s. They are effectively descendants of the old single-player text adventure games, such as Zork and Adventure, except that they allow many players from around the world to interact in the game world. Many MUDs are primarily focused on completing quests, solving puzzles, killing monsters or fighting other players. A smaller niche are devoted to roleplaying and interactive storytelling, along the lines of a text-based LARP (Live-Action Roleplaying) game.