Active Worlds is an online virtual world platform where users can interact and build shared environments. Players can visit a wide variety of official and user-created world servers. The primary world, Alphaworld, features an enormous sprawl of myriad towns and subcommunities that has been collaboratively constructed since the 1990s. Other worlds include the cyberpunk-themed Metatropolis and worlds themed after Mars and Yellowstone. The game is free to play and features a virtually endless amount of territory to explore.