Adding online play to a turn-based game usually stalls on infrastructure rather than on gameplay. The moment you decide two people should be able to play your chess or card game from different machines, the conversation turns into websockets, a persistent process, a host that will keep that proc...
Source: [Dev.to](https://dev.to/paulcrinigan/a-turn-based-multiplayer-server-that-fits-in-one-php-file-15l6)