I wrote an entry level blog post about Cashu 🥜 for nostr:npub122pnqy3sxlnghaxarll4rywx2jy5d2vf2a52pdguzmdea4wlupesdpvsgz

Dive into Cashu, its history and some of the core ecash concepts: https://www.blocktrainer.de/en/blog/cashu-the-open-chaumian-ecash-protocol-on-bitcoin