Relativity was shared on HN a while ago. I can't speak to the quality of the hardware as I haven't tried it, but it fits your requirements, partially. For various reasons (and please correct me if I'm wrong) all VR compositors are tied directly to a store/platform because everyone has an appstore in 2020. wxrc (Wayland VR compositors) is in development but it looks like it's not quite ready for wide usage. That means PCVR is still mostly directly tied to Steam and standalone VR is mostly tied to Facebook...