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.
SuperNotecard - Introducing SuperNotecard. SuperNotecard is an online writing tool that features virtual notecards to help arrange facts or scenes, track details, organize paragraphs, and clarify your composition process.
Memrise - Learn a new language with games, humorous chatbots and over 30,000 native speaker videos.
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Quizlet - Quizlet allows you to review and create flashcards for a variety of subjects, such as math and reading.
Freeplane - Freeplane is a powerful and free software for building mind maps.