Relativty: An open-source VR headset for $200

From the GitHub this is only capable of 3DoF tracking, which puts it in the same category as the defunct Oculus Go headset, or Google Cardboard. 6DoF is really the bare minimum to qualify as proper VR nowadays.

For the uninitiated 3DoF means the headset only tracks the rotation of your head, not your heads absolute position as you move around, while 6DoF tracking does both. 6DoF is also much harder to implement.

3dof is sufficient, imho, for a large number of VR use cases, because most people don't have a full room dedicated to it, but is at a desk. Sitdown VR setups would be more common, if the equipment was cheaper.