OpenSimulator!

The WhiteCore server is an OpenSim/Aurora-Sim derived project with heavy emphasis on supporting all users, increased technology focus, heavy emphasis on working with other developers, whether it be viewer based developers or server based developers, and a set of features around stability and simplified usability for users.

Build multiuser 3d scenes using html-like tags and javascript. SceneVR scenes are viewed using a browser-powered viewer (powered by webGL). Chrome, firefox and IE are supported. The server is powered by node.js and runs on Windows, Mac OS and Linux.

In Twinity's free 3D world and 3D chat community, you can create your own avatar, party with friends, dress-up, go shopping and interact via 3D chat and animations. Get creative and design your virtual apartment in an authentic real virtual city or create your own island to host parties, flirt and lead an extraordinary life! Join now and discover the possibilities of Twinity's virtual universe.

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!). You can then move about, play online games, shop and make friends with people from all over the planet. You can even stake claim to a piece of land and build your own virtual home, mansion, estate or castle! If you like to travel, there is plenty to explore.

Finally, a community-based virtual world filled with actual games and entertainment made by people who love creating games.

vSide is an immersive, interconnected virtual city environment where you can hang out, listen to music, chat, dance, and make friends.