nostr:npub1l2vyh47mk2p0qlsku7hg0vn29faehy9hy34ygaclpn66ukqp3afqutajft's NIP-60 is gaining traction. There are at least six different Cashu wallets that have support for NIP-60 

NIP-60 specifies how to store ecash on nostr relays. This allows you to use the same ecash balance with different wallets or on different devices. You log in with your nsec and your ecash balance pops up.

I thought wallet synchronization is going to be a major challenge for Cashu wallets but it seems nostr devs have already solved the issue.

Very impressive.