boardgame.io
State Management and Multiplayer Networking for Turn-Based Games
...This abstraction lets developers focus on the rules and mechanics rather than on networking, persistence or UI plumbing. It supports both local games and online multiplayer across clients, and can be used with different view layers — e.g., vanilla JS or a UI framework like React or React Native. It also offers tools to help with prototyping, debugging, logging, replaying game states, and even simple AI bots. Because of its simplicity and flexibility, boardgame.io is widely used for rapid prototyping of new game ideas or building full multiplayer board games.