VeeR VR - Global VR video community
Firestorm Viewer - Firestorm is to Virtual Worlds what Firefox and Google Chrome is to the Internet. We develop and distribute an open source viewer for accessing Virtual Worlds.
VRChat - Create and play in virtual worlds with others
Second Life Viewer - Download Second Life from the official site here.
Spatial - Collaborate from anywhere in AR
Kokua / Imprudence - Kokua is an open source viewer for Second Life and OpenSim-based virtual worlds.