Anki looks good, though it seems like a lot of work - would be good to have a community made effort for things like Elixir and Phoenix 
Personally I use good old fashioned pen n paper 
Whenever I am reading a book about a topic that I really want to grok, I make notes whenever I come across anything I need to remember that I don’t already know. Then, before starting the next reading session I read through all the notes first. As I progress through the book, I start skipping my earlier notes - or only review them periodically. I find this really works for me.
This thread may also be of interest:
