Yeah, fedimint being federated is the big difference. I feel like its not really a protocol as much as a method of using cryptography.

Cashu is mostly Python where Fedimint is mostly Rust, also.

I really reccomend checking out this video on the subject:

The video is called "Chaumian eCash in Bitcoin - Cashu and Fedimint"

Its a presentation by Adam Gibson and he gives a really good overview on eCash in general as well as sections on both Cashu and Fedimint.