Anki - 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.

Stack Overflow - Community-based Q&A part of the Stack Exchange platform.

Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.

The Answer Bank - The Answer Bank is the UK’s leading question-and-answer site.

Kartka - Kartka is a flash card learning tool with real-time sync, spaced repetition algorithm, and a modern and friendly interface.

Blurtit - Blurtit is a Q&A website. You can ask a question or answer on any question.