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.
Cram - Cram is an app for Android, Windows and Apple devices that allows you to search for flashcards in a range of topics to study for an upcoming test or to learn new information. Read more about Cram.
Simply Learn Languages - A phrasebook of 50+ languages for traveling (with audio)
RemNote - All-in-One Tool For Thinking & Learning
LearnObit - A tool for your learning, like Anki & Workflowy in one
The Mnemosyne Project - Mnemosyne (named for the Greek goddess of memory, Mnemosyne) is spaced repetition software...