OpenVR

OpenVR is a software development kit (SDK) and application programming interface developed by Valve for supporting the SteamVR (HTC Vive) and other virtual reality headset (VR) devices. The SteamVR platform uses it as the default application programming interface (API) and runtime. It serves as the interface between the VR hardware and software and is implemented by SteamVR.
Although OpenVR is the default SDK for HTC Vive, it was developed to have multiple vendor support. For instance, a developer can design OpenVR-based trigger button functions for controllers of Oculus Rift or Windows MR because these systems are both supported by the SDK.
Valve has announced that they will be cooperating with the Open Source Virtual Reality (OSVR) project, although the extent of the cooperation is unclear.