Are you familiar with Niklas Luhmann’s “zettelkasten” methods? Seems like there might be some fertile ground at the intersection of these two ideas...
Additionally, his system does have spaced repetition built-in, too:
"I’ve embedded a Spaced repetition memory system into my notes: The mnemonic medium can be extended to one’s personal notes. This has substantially changed the medium, but in ways I don’t yet understand very well."
I do not believe he has open-sourced his note taking system, but it is fun to browse around in; he presents a lot of interesting ideas, particularly if you're into this space.
He is using Bear, you can find on youtube how he creates those notes.