I'm working on this problem myself [0]. The app allows you to map out topics of interest as though making a mind map, building out subtopics that are as specific as needed to really become acquainted with an area of knowledge. And later on you'll be able to come back and refresh your memory about what you reviewed, and possibly drill down into some of the articles people recommended but you didn't have time to read at the time.
Interestingly, I chose the name "Digraph" independently of the repo that a sibling comment refers to, after observing the way the topics relate to one another.
The "knowledge graph" and "personal knowledge base" community is working on it! Although in a lot of little projects; nothing unified that I know of. Here's a project I worked on for a while, which lets you maintain a Neo4j database via an Emacs frontend:
One way of course, is using your internal memory. But it's rather limited. Unless you're buffet like.
But what about creating an external memory ? Maybe not as usefull as your brain, but much more usefull than Googling ?
I've tried to do so with evernote. It somewhat work. But surely , it's not the person best that's possible.