Just found Kinnu, an iOS and Android app. Looks neat. Gives you a knowledge map of courses with topic overviews. It's like Duolingo for topic overviews. You answer questions over spaced repetition.
Just a team of 5 including ex-Googlers. Founders are really open and talking to everyone on Discord.
Definitely go on the Discord and make suggestions. Saw them saying they'll add a Paul Graham's essay path to the app soon, so very excited about that!