About Disappearing Tic Tac Toe
How to Play
It's just like regular Tic Tac Toe, except each player can only have three pieces on the board at once. When you place your fourth piece, the oldest piece disappears. You can tell the order in which the pieces will disappear based on their size. They start out big and then get smaller until they disappear.
Since you can only have three of your pieces on the board at any given time, that means in order to win, you need to place three pieces in a row/column/diagonal sequentially.
Notes on Optimal Play
I have strongly solved Disappearing Tic Tac Toe. With optimal play, the first player can force a win by going in an edge spot. If she goes in any of the other spots, with optimal play by both players, the game will go on forever.