OpenVR is the underlying SDK in making many of the VR head-mounted displays (HMDs) work with Unity and will likely keep growing in importance. Much of the VR work at ThoughtWorks was built on top of OpenVR, because it will run on any HMD, unlike the other SDKs. Though it is not open source, it is free via the license. The Oculus SDK is more restrictive in its licensing and only works on Oculus devices. OSVR, while truly open source, doesn't seem to have as much adoption yet. If you're going to develop a VR application and target as many devices as possible—and not use Unity or Unreal to develop them—OpenVR is the most concrete and pragmatic solution right now.

OpenVR is the underlying SDK in making many of the VR head-mounted displays (HMDs) work with Unity and will likely keep growing in importance. Much of the VR work at ThoughtWorks was built on top of OpenVR, because it will run on any HMD, unlike the other SDKs. Though it is not open source, it is free via the license. The Oculus SDK is more restrictive in its licensing and only works on Oculus devices. OSVR, while truly open source, doesn't seem to have as much adoption yet. If you're going to develop a VR application and target as many devices as possible—and not use Unity or Unreal to develop them—OpenVR is the most concrete and pragmatic solution right now.