Most exciting projects I can think of atm are Chaumian Ecash systems like Fedimint and especially Cashu.
(For more info see: https://docs.cashu.space/ )
It does have tradeoffs but is just so easy to transact with it, while being quite private. Also implementing it gets easier and easier and it keeps getting more usecases, zo i can really see this taking off. Example: https://nitter.at/callebtc/status/1632076885441085445#m