Twinity!

Miitomo is an app from Nintendo that brings out a side of you your friends have never seen before!

OpenSimulator is an open source multi-platform, multi-user 3D application server. It can be used to create a virtual environment (or world) which can be accessed through a variety of clients, on multiple protocols. It also has an optional facility (the Hypergrid) to allow users to visit other OpenSimulator installations across the web from their 'home' OpenSimulator installation. In this way, it is the basis of a nascent distributed Metaverse.

A 3D internet chatroom application for chatting with friends and meeting new people

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.

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