BidTacToe is tic-tac-toe but you bid on the squares. Every turn begins with one player selecting a square that will be up for auction. Each player then submits a bid.
The winner gets to put their letter down in that square. You lose your bid, even if you don’t win the auction. Once you get three in a row, you win.
I built this as a Phoenix LiveView app. It’s all open source — here’s the code.