The quick summary: Anki is a very cool computer program that helps you learn things, and retain what you've learned.I'm going to talk about it mainly with regard to memorizing Japanese kanji, but it can be used with any sort of memorizable fact.
The history: Way back in the 70's, some smart Northern Europeans were sitting around thinking about the forgetting curve, the decline of memory retention over time.Basically, this is the law that says that if you don't review something, you'll probably forget it. While one can delay the forgetting is through mnemonic techniques (stories, memory caves, associative devices, etc.), it can also be prevented through repeated review of the material. The more you review something, the longer it sticks in your head. This is pretty intuitive; I know the multiplication tables by heart because I've seen them so many times.
From Anki's website:
Anki is based on a theory called spaced repetition. In simple terms, it means that each time you review some material, you should wait longer than last time before reviewing it again. This maximizes the time spent studying difficult material and minimizes the time spent reviewing things you already know. The concept is simple, but the vast majority of memory trainers and flashcard programs out there either avoid the concept all together, or implement inflexible and suboptimal methods that were originally designed for pen and paper.
While Anki can be used for studying anything, it also ships with special features designed to make studying Japanese and English easier: integrated dictionary lookups, missing kanji reports, and more. Sample decks are also provided for Russian.
Anki's scheduling algorithm is based on the proven SM2 SuperMemo algorithm. It improves upon the basic SM2 algorithm by adding features like priorities and a revision queue sorted in order of priority.
There are other programs out there that do the same thing; Mnemosyne is probably the most popular. Here are the reasons I like Anki better (the author also has a very nicely written "Why Anki?" page):
-The interface is very zen. Here is how you use Anki to review flashcards:
1) Open program
2) Look at expression/question/prompt
3) Do you know the meaning/answer? Hit the spacebar and check.
4) Rate how well you remembered it from 0-5. Zero indicates that you've never seen it before, 1 represents a mistake, and 2-4 are for rating how easy you remembered it.
5) There is no 5.
It takes care of everything for you. If you keep rating cards zero, they'll keep popping up. Rate a card highly more than once, and the interval will get longer and longer. Make a single mistake on a card you know pretty well, and it won't reset all your progress; you'll see it again in a little bit, and depending on how hard it is then, it could come back in a day, a week, or a month for reinforcement. The system is smart, easy, and effective- I'm scoring about 80-90% across 700 vocabulary cards covering two months of classes.
-It auto-generates Kanji readings, making creating Japanese vocabulary decks very simple. It can also look up meanings for you (though you need to be online to do this; I just use Apple's dictionary).
-My flashcard deck, and all the review work I've done with it, syncs between a desktop client, a mobile (and regular) website, and my iPod. This means that no matter where I am, or what gadget I'm carrying, I can review material.
-The community around it is innovative, helpful, and fun. When I started using it two months ago, the iPod client required hacking into your ipod, and compiling a local webserver inside itthat pretended to be the Anki site. Now, you can do it with a simple one-click-install plugin for the desktop client (no jailbreaking required). I found a bug in the latest release that was making it impossible to sync decks correctly, and the author of the plug-in had it fixed within a few days.
Note for people currently in a Japanese class:
In terms of learning for learning's sake, the only Kanji abilities that really matter are Kanji->Reading/English, and English->Kanji. In the real world, you will never come across a situation in which you need to turn kana into kanji for the achievement of some greater goal. That said, many Japanese classes have tests with this format (a sentance with an underlined hiragana word we are expected to kanji-ize), and Anki is not set up for this out of the box.
You're going to want to grab this file, and use it to start building your deck; I've modified the basic Japanese model with two more card models. One goes from the reading to the meaning and kanji, and another goes from the reading and meaning together to the kanji. While the first might seem more like your tests, as you learn more kanji with the same reading, it will become pretty useless.
Note that there is no current way to modify the models of a deck in progress. You'll need to import all your cards to this deck, which will unfortunately void the reviews you've done up to this point. Don't sweat it, though- just keep rating cards you know highly, and it will sort itself out.
Use the "active tags" menu to control which models you're reviewing, so that you don't have to study production cards for Kanji you'll never need to write.