For my C++ class I had to make an unbeatable Tic-Tac-Toe game, so I decided to translate it from C++ to Scratch. This is the result, I used smart solving for all of the easy decisions and included all of the other variations. Just move your mouse to choose the square you want to play in and click to place your "o".
Please report any outcomes I haven't solved for (there might be some, I'm not sure). This is also 100% Pen :P