amark/gun

GUN is an open-source JavaScript database and synchronization library designed for decentralized, peer-to-peer applications. Most databases live on a central server that everyone connects to. GUN flips that model: data can be stored and synchronized directly between users' devices (browsers, phones, servers) in real time, with no central server required, though you can use relay servers to help peers find each other. It stores data as a graph (a flexible structure that handles not just simple key-value pairs, but also tables, nested documents, and relationships between pieces of data). Changes made on one device automatically propagate to all other connected peers instantly. It also includes built-in end-to-end encryption, meaning data can be secured so only the intended parties can read it. You would use GUN when you are building an app that needs real-time collaboration between users (like a chat app, shared document, or multiplayer game), when you want the app to keep working offline and sync when connectivity resumes, or when you want to avoid dependency on a central cloud database. It runs in both the browser and Node.js, is installable via npm, and describes itself as a decentralized alternative to services like Firebase.