Last year I ran an experiment where I would do Duolingo but ONLY in my spare time.
5-30 minutes per day but only when I'm waiting in line, having a cup of coffee , or driving my car on the highway (just joking about that last one).
After about a year I realized that I had a passable understanding of German.
Mind you I did this in my SPARE time... so it was basically like I had a super human skill.
Instead of knowing the latest and greatest gossip about Google (which would be irrelevant in a year) I now had a passing understanding of a new language!
I became pretty convinced that I did NOT want to invest any more time learning anything without having a spaced repetition system.
I started using Anki but honestly I found it really rough.
I tried to figure out a way to use PDFs and web content and work with Anki but it was a massive pain having the two systems completely separate.
If I could integrate them I figured I'd have the holy grail!
I started working on a basic proof of concept which ended up taking me 4-8 hours a day for the last six months:
It's still getting there - not perfect yet.
But it supports full PDF and HTML documents, annotation, and sync to Anki.
You can create flashcards while you're reading and don't have to switch apps.
You additionally keep the original context (where it was found, etc).
It also allows you to keep everything in one place. All your books. All your notes and flashcards.
It supports Anki sync via a plugin so if you're already using Anki you can push new flashcards to it directly.
It's not as user friendly as I would like. I'm actively working on that part now. It's more an Open Source project than a product but I'm rapidly polishing it to make it more usable.
If you guys like it but it's not perfect drop me a line and I usually prioritize user bugs.