Which Microsoft mixed reality headset was first released in 2016?

The Microsoft mixed-reality headset first released in 2016 was Microsoft HoloLens. Its Development Edition began shipping on March 30, 2016, initially targeting developers in the United States and Canada. HoloLens was designed as a self-contained head-mounted computer that could place digital objects into a user's view of the physical world.

Unlike conventional virtual-reality headsets that largely block out the surroundings, HoloLens used transparent displays, cameras, spatial mapping, gaze, hand gestures, and voice commands. Microsoft built it around Windows 10 and its Windows Mixed Reality platform. The headset's technology also drew on work associated with Kinect, Microsoft's motion-sensing accessory for Xbox consoles.

The 2016 release was a development product rather than a mass-market consumer launch, which explains why some sources describe HoloLens as announced earlier but released later. Microsoft announced HoloLens 2 in 2019, with a larger field of view, improved hand tracking, and an enterprise focus. The competing options in this question were virtual-reality products from other companies, not Microsoft's mixed-reality headset.