Anki -- an easier way to study almost anything
Anki’s developer describes the project as "a program which makes remembering things easy". That sounds a little vague, but it's also very accurate. Anki is a smart and versatile flashcard-based tool which really can help you remember just about anything.
The program allows you to create, download and edit flashcards. Each card has a question on one side, its answer on the other. This could be simple text -- a deck on capital cities might use "France", "Paris" -- but Anki also supports graphics, audio, video, even scientific markup (via LaTeX), so there's plenty of scope to be inventive.
When it's time to study, you're shown each card. When you think you've remembered the answer, press the spacebar to check. Finally, you get to rate your own answer based on its accuracy, and how easy it was to remember. Cards you got right will be shown less frequently, and Anki will instead focus on anything you can't remember.
If you're unused to flashcards then this can seem complicated, and there are plenty of rules, options and settings to learn.
Fortunately many existing Anki users have created and shared decks covering everything from "Mandarin Chinese" to "IATA airport and city codes", "Actor and actress pictures" and "Applied anatomy and physiology" (explore the full list here). You can freely download and try out anything of interest, a quick and easy way to learn the program basics.
Better still, there are Anki builds for Windows, Mac, iPhone, Android and Linux, so you can continue your studies just about anywhere. And there's even a free service to keep cards in sync across all your devices. (Note, though, the iPhone build is a commercial product and costs $24.99.)
Anki takes a while to learn, and the desktop interface desperately needs a revamp. But the program scores where it matters: the core technology is excellent, it's enormously configurable, and there are lots of shared decks and add-ons to explore.