OpenSimWorld is described as 'Directory of 3D worlds connected through the hypergrid'. There are more than 10 games similar to OpenSimWorld for a variety of platforms, including Windows, Mac, Linux, Oculus Rift and HTC Vive. The best alternative is Second Life, which is free. Other OpenSimWorld like games are VRChat (Free), OpenSimulator (Free, Open Source), ActiveWorlds (Free) and IMVU (Freemium).
Imagine a world where anything is possible. Join a game of capture the flag in outer space. Share stories around a campfire while roasting marshmallows, then moments later experience a retro game of bowling with an alien and robot.
Activeworlds hosts a Universe of over 500 3D virtual reality worlds. In these worlds you can choose from a vast array of avatars that fit your personality (or your perceived personality - that's half the fun!).
The Open Simulator (OpenSim) project is developing an open source simulator that is compatible with the Second Life viewer, but opening up innovative applications centering on a virtual three-dimensional world.
AltspaceVR is a social VR platform for meeting people from around the world, playing interactive games, and attending free live events. Choose from over 28 activities or attend live events with comedians, DJs, authors, celebrities, and more.