It's a Chaumian Ecash layer 3 protocol built on top of lightning network. Allows private monetary exchange in communities even when offline. Requires trusted third party in a form of a mint ( a server?). You can create your own mint or use a mint of somebody you trust (or not). This description is more of a Cashu description, but from what I heard it's almost the same as Fedimint. The biggest difference is that Cashu is already running. If anyone knows better, please correct me 🙏