99 Blocks is a twist on the traditional block stacking game of Tetris. Instead of stacking blocks to clear lines your objective is to create the highest tower you can with just 99 blocks. The twist is that this is a Tetris variant with physics. So if you don't stack carefully, your tower will fall.
I myself have come back to 99 Blocks a few times after first playing it to try out different stacking strategies, but ultimately 99 Blocks remains a very casual experience with possibly a too steady pace of gameplay.