No idea, haven't gone down that particular rabbit hole yet. Ive heard that Cashu might be the most practical for now, but it's very early for Bitcoin backed ecash. 

 Im ready to learn! 
https://github.com/cashubtc/awesome-cashu 
https://github.com/fedimint/awesome-fedimint

Where else should I look? @calle 👁️⚡👁️