As mentioned in thing 51, I've been working on a playable version of Haft Schroedinger Chess. I've come across a one other implementation here, but that implementation is not true to the full rules of the original description: it puts every piece including pawns into superposition at the start, whereas pawns are not supposed to be, and it also doesn't account for entanglements arising from checks. I made this implementation to solve those problems.
It tracks entanglements from checks invisibly though, since I was uncertain how to conveniently display them. I want to improve the UI quite a bit, but that will come in time. I also wanted to make art for each of the 31 valid piece-superpositions, but that will also come in time. I also want to eventually make it playable over the internet. If you notice any bugs, please reach out to me.