The main open XR project is called Monado and it implements Khronos OpenXR:

https://monado.dev/ https://www.khronos.org/openxr/

What is MR?

Microsoft's brand for their platform which covers both VR (their confusingly named Windows Mixed Reality range of VR headsets) and AR (eg. HoloLens).

MR and AR are essentially equivalent in the "industry". MR is Mixed Reality. For "mixing" digital images with the real world.

Mixed reality

Doesn't AR also mean Mixed since it's augmented?

I think that’s a _really_ fair question! xD

I’ve heard “mixed reality” being used to refer to the continuum between reality - augmented reality - virtual reality. In the above question I’d read it as asking about the state of problems particularly pertaining to the transitions along this continuum. (Made up example: of you solve locomotion in VR by putting people on moving belts, a problem in MR would be how to transition someone from walking around in unobstructed reality to walking in VR. I don’t know if that’s a real problem—please take it just to illustrate what I mean.)

Edit: Wikipedia’s article on MR includes a whole section on “differences in terminology”! \o/ https://en.wikipedia.org/wiki/Mixed_reality They also use the word “continuum”, but don’t seem to directly back up my further claims about using the word to refer to problems arising specifically at the interface of AR/VR.

I believe Mixed Reality was a term coined by Microsoft to differentiate their products, basically a marketing term.[1]

[1]https://www.vox.com/2015/7/27/11615046/whats-the-difference-...