Logseq (open source): https://logseq.com/
Roam Research: https://roamresearch.com/
At the moment everything gets hosted locally unfortunately. I was planning on polishing it so that it's easier to setup. Then I can put it on a Show HN in the future as a kind of "how this was built" :) and give some inspiration to other people who thought of building their own.
“What I cannot create, I do not understand.”
“Once I asked him to explain to me, so that I can understand it, why spin-1/2 particles obey Fermi-Dirac statistics. Gauging his audience perfectly, he said, ‘I'll prepare a freshman lecture on it.’ But a few days later he came to me and said: ‘You know, I couldn't do it. I couldn't reduce it to the freshman level. That means we really don't understand it.’“
His book Surely You're Joking, Mr. Feynman! also has a couple of anecdotes where he solves people's problems by asking them questions and trying to understand them. Unfortunately I read this some time back and the exact page numbers escape me.
Generally, if you search for Feynman Technique you'll find anything in the direction of "explain it to someone to understand", but I think there is a lot of misattribution going on here. Like Einstein, people love to stick his name on things.
And finally, an indirect, but in my opinion well-summarized reference to the way Feynman learned, was in the Richard Feynman section of Lex Friedman's 118th podcast [1].
[0] https://en.wikiquote.org/wiki/Richard_Feynman#Quotes
[1] https://youtu.be/U_6AYX42gkU?t=452 (with exact starting time)
The best learning experiences I've ever made were with the "digital gardening" method explained in the article. Especially the process of writing down what I'm trying to understand and putting it in my own words is hugely beneficial. That old trick of Feynman's where you take a topic you don't understand and explain it to someone – be it a person, your personal wiki or just a text note – really works wonders. And revisiting a note and changing it a bit also seems to reflect how we remember things: Not regurgitating them, but reliving them.
Apart from that I found the process of creating my own personal wiki highly rewarding and can only recommend it to others (if you have the time). It's an absolute joy to use something you've made and explain the creation of it to yourself using it.
In my case I've also made the wiki in such a way that I can add exercises to notes and then do spaced repetition on those (which was also a blast to implement). The exercises themselves can be functions so that things get mixed up from time to time. I don't often do the exercises, but the process of creating them adds another layer of understanding from my experience.
Edit: Continuation...
But this is just me getting excited over the personalized wiki I've created.
The article importantly mentions that "there is no one-size-fits-all app" to best understand something, so it takes some time and experimenting to figure out what works best for you (heck, I think I went through at least 5 iterations of note-making systems before I settled on this one for about two years now). And since we're on HN, I think everybody here has the skills to make their own.
I really wish schools would add a dedicated, mandatory subject about learning to learn. It would have saved me a lot of time I wasted back in Uni and afterwards just trying to figure out how to quell this urge to retain information.