By the end of the year, or perhaps in 2015, the Oculus Rift virtual-reality headset will launch as the most hotly anticipated gaming peripheral in years. About 50,000 Rift headsets are in circulation among developers working on applications for the hardware, and the company just announced a new and improved dev kit at the Game Developers Conference. Meanwhile, Sony is promoting its new Morpheus virtual-reality headset, and there are other entries on the horizon.