untris is a clever take on the classic puzzle game Tetris, where players are supposed to figure out the sequence of events that led to how the tiles are arranged as it is. This means doing everything in reverse, removing tetrominoes and adding horizontal lines until the entire well is cleared. Tetrominoes can be rotated using the Q and W keys, and you have unlimited undos in which to reset all of your previous moves until you’re back at the starting point.
Judging by the comments it doesn’t seem like anyone’s beaten the game yet, but you’re welcomed to give it a go and find out if you’re just as good at Tetris when you have to play it backwards. untris can be found hosted at increpare’s site.