One of my ideas for a toy project is Schrödinger´s Chess or perhaps Quantum Chess:

when you move a piece, you can move it to any and all possible squares at the same time - your piece is on all of the squares you've placed it, so in your opponent's next move they can eliminate your piece by attacking any of the positions it's currently in.

In your own next move, you can move the piece from any of the positions it's currently in and place it in a new set of positions.

Eliminating or moving a piece removes it from all positions it's currently in.