I worked on something similar a while ago. First I also looked into building something more visual/map like but after many iterations I got frustrated by the lack of overview one had for more complex maps. So I pivoted to a more TOC/text based version. It was supposed to be community driven but when I finished my studies, the app lost the utility it once had to me. But it's still up & running:

https://owleo.herokuapp.com/concepts Source: https://github.com/Gregoor/owleo

A startup that also takes the visual learning map route is Expii: https://www.expii.com/