RakNet is a multi-player, game network engine. RakNet provides networking support for C++/C# game engines in a high performance and cross-platform manner with easy integration. RakNet is used by Unity, Havok, Mojang, Sony Online, and many other game studios. The RakNet acquisition is interesting for Oculus, though they have used the software internally for years. In acquiring RakNet, they've open-sourced this middleware software under a modified BSD license.
The RakNet source code is opened up under OculusVR on GitHub. Details on the acquisition and new Oculus Connect conference can be found via the Oculus blog. More details on the RakNet software can be found via Jenkins Software.