Yjs

A high-performance CRDT implementation for building local-first, real-time collaborative applications.

Yjs enables seamless shared state across distributed clients using Conflict-free Replicated Data Types (CRDTs). It powers collaborative features in platforms like JupyterLab and Hocuspocus by syncing data types (arrays, maps, and text) with sub-millisecond local updates. The framework remains network-agnostic: you can plug it into WebRTC, WebSocket, or Matrix providers to handle concurrency without a central authority. Its performance scales to thousands of operations per second, making it the industry standard for robust, conflict-free peer-to-peer synchronization.

https://yjs.dev