(Repost from someone else)

Anki is a program which makes remembering

things easy. Because it's a lot more efficient than traditional study methods, you can either greatly decrease your time spent studying, or greatly increase the amount you learn.

Anyone who needs to remember things in their daily life can benefit from Anki. 

Since it is content-agnostic and supports images, audio, videos and scientific markup (via LaTeX), the possibilities are endless.

For example:
-Learning a language
-Studying for medical and law exams
-Memorizing people's names and faces
-Brushing up on geography
-Mastering long poems
-Even practicing guitar chords!

https://apps.ankiweb.net/

And it is free!