Cashu is chaumian ecash built on bitcoin
You send a lightning payment to an ln node that issues you an ecash iou
The ecash offers custodial but near perfect privacy for spending amd receiving ecash
You can send ecash tokens via nostr dm, text message, email etc

https://github.com/cashubtc/awesome-cashu 

 Interesting stuff being build. Regulators regulate and #nostr people build!