Comment by MrRadar

It's... slightly complicated. In theory OpenVR is "open" in the same sense as OpenGL in that it is an open API that anyone can implement (but which doesn't have a standardized open-source implementation). However right now that aspect of it is just theoretical since the only runtime implementation of OpenVR is the SteamVR runtime (which is only distributed through Steam) and Valve are solely responsible for defining the API (there's no equivalent to the Khronos Group for OpenVR).