Tic-Tac-Tetris

V1:

In this Tic-Tac-Toe and Tetris mix, both players must put down the greatest number of marks to form Tetris blocks, the player who accumulates the most by the end wins.

To set up, get a piece of paper and a pencil then make a 7x7 Tetris board. Just like the original, the two players must choose between an X or O to represent each other. Each Tetris block requires four spaces to be filled and can be done in any rotation. Each player can cut off the others attempt to form blocks, similarly to the original Tic-Tac-Toe. When one block is fully formed it must be signified by a line crossing through it. If necessary, a legend can be made showing all the blocks that can be formed, different angles of the blocks are not required to be put in the legend. 

When the board has no more space available for more shapes to be formed, the amount of blocks formed shall be counted, and whoever has made more by the end wins.

V2:

Any grid between 5x5 and 9x9 will work well enough for the game.