https://tictactoe.joshchang.co/
This is a web-based implementation of the game Ultimate Tic-Tac-Toe. It consists of nine regular tic-tac-toe boards arranged in a 3x3 grid, forming a "meta-board." Players take turns placing their mark (X or O) in a cell, but the twist is that the cell they choose dictates which local board the opponent must play in next. If that target board is already full or won, the opponent can play anywhere. Each local board follows normal tic-tac-toe rules, and winning one gives control of that square on the meta-board. The first player to win three local boards in a row (horizontally, vertically, or diagonally) wins the game.
You can read more about it here https://en.wikipedia.org/wiki/Ultimate_tic-tac-toe.
I made this because existing online implementations are ugly and don't let you confirm your move which is annoying in practice because it is easy to misclick, which can ruin the whole game.
It uses websockets for live gameplay.
Ultimate Tic-Tac-Toe is quite challenging to play because it really messes with your spatial intution. Give it a go!