It 'a shame that after a few weeks / months I have read a book or an article I can remember only 20%!
To store all the key concepts of a book it's a must review it time-to-time, this will secure the long-term memory.
This program works like this:
1) read the article or chapter highlighting the keywords of each section
2) re-read the keywords mentally reconstructing the main concepts
Optional: 3) creates a mind-map with your hands and memorize it
4) after one hour review it
5) enter on this app the name of the chapter or article, so you can re-find it, such as "Leader of yourself, chapter 1" and press "Remember it!"
6) every day you open the app to see if there is something to review. If it is indicated under "Today you must review:" review it and when you will have all the concepts in mind you can click "Done!".
The app will remind you of everything inserted after one day, one week, one month, six months and every year.
(This sequence is the result of some scientific studies, I have not decideded it myself!) ;-)
How nice, think, your books in your mind, FOREVER!