OpenVR is an API and runtime that allows access to VR hardware from multiple vendors without requiring that applications have specific knowledge of the hardware they are targeting. This repository is an SDK contains the API and samples. The runtime if under SteamVR in Tools on Steam. 

Documentation for the API is available in the wiki: https://github.com/ValveSoftware/openvr/wiki/API-Documentation

More information on OpenVR and SteamVR can be found on http://steamvr.com