In Ultimate Tic Tac Toe (also known as Super Tic Tac Toe or Meta TTT) each square of the traditional board contains a smaller tic tac toe board. Two players take turns playing the smaller boards until one of them wins three in a row.
Changes and improvements are more than welcome! Feel free to open a pull request if you have any improvements in mind.
Super Tic Tac Toe is licensed under the CC BY-NC-ND 4.0 license.