https://twitter.com/mii8080mii
https://miivrc.booth.pm/items/1982460

If you weren't tired of all the new FBT solutions coming out, here's another one. This uses 3 smartphones, each emulating a tracker. I'm guessing it's using ARCore/ARKit on Android/iOS, since it's using the cameras to do inside-out tracking. So I guess if you just happened to have 3 compatible smartphones just lying around, you could try this out.