I've been looking for and trying to come up with a system to store and keep track of knowledge for a long time, and I was wondering if maybe this was already a solved problem for others that I just so happen not to know how to put in a search engine.

What I mean by knowledge in this case is, roughly, "information that is useful, but that is hard to remember". Not necessarily hard as in "complex", but rather due to not using that information often enough to make it stick in memory.

Ideally, such a system would allow me to store collections of things that can be articles, videos, particularly interesting podcast episodes, papers, book excerpts etc. in a way that is easy to search and logically meaningful. I would like to be able to insert the things that I already consulted, and those that I plan on delving into in the future.

To give a concrete example: I plan on learning about Machine Learning in the near future, and I would like to have a way to save all the material I come across to almost on a daily basis, in order to have it readily available when the day will come that I will need it. Saving it in bookmarks is a recipe for failure, as bookmarks never worked for me. I have tried (and still try) to keep a hierarchy of files and folders were I save stuff, but that is definitely not easy to consult in any way, since it doesn't allow me to easily tag resources or make notes about them that are easy to search.

Do you have any recommendations?