NOTE: I now document my favorite iOS apps for studying Japanese in the directory: http://www.mondaiji.com/directory/entries/category/view/64-japanese-study
The Best Apps
If you plan to study Japanese (or any foreign language for that matter), you have loads of new words to learn. You're gonna need a solid flashcard program. Sure, there are Japanese-specific study programs that have volumes of included flashcards, but there's a significant memorization advantage to making your own customized flashcards. Namely, the words you'll study are relevant to your current Japanese study--they're words you're working on and/or covering in class.
I tried a bunch of highly-rated flashcard app demos before settling on Flashcards Deluxe because it was the only one I found with a critical feature I was seeking. It allows you to create cards with up to 5 "sides." So I put the kanji on side 1, furigana on side 2, meaning on side 3, and a mnemonic hint or note on side 4 (if I can come up with one). This feature alone sold me on Flashcards Deluxe, but awesome also is the "spaced repetition" study algorithm and ability to import cards via the developer's website.
Flashcards Deluxe is now my go-to app for studying Japanese vocabulary.
Japanese Sensei Deluxe
by Cole Zhu Inc.
NOTE: This app has finally been updated and improved, so I can once again highly recommend it.
Of all the vocabulary-building apps I've tried, this one is a lustrous diamond. Most similar apps just take an open source Japanese dictionary and turn it into flashcards. I didn't have much luck memorizing new words with these apps, and they were about as fun as reading the dictionary. JSensei Deluxe breathes fresh air into this ubiquitous approach--the lessons are well-constructed with sample sentences, and there's a quiz at the end of every lesson. It remembers the words you've been struggling with and pops them into the quizzes, even if the words were from previous lessons.
In fact, the quizzes are probably the best feature because they don't just cover the words from the selected lesson. If they did, you'd probably pass them easily due to the recency effect (having just studying them). Instead it challenges you with words from all previous lessons, keeping track of how well you know the words from each.
And if all that wasn't enough, this app also includes native-speaker audio pronunciations. It's one of the pricier Japanese study apps, but well worth it in my opinion.
by Sukolsak Sakshuwong
Every student of Japanese needs a dictionary app. Honestly, I was hesitant to buy one since the free Imiwa dictionary app is superb. But Midori comes with an unmatched, hard-to-find feature--integrated handwriting recognition. Often I found myself shopping in Tokyo perplexed by an unfamiliar kanji on a product label. With Imiwa I was out of luck. But with Midori I can sketch the kanji with my finger and (if I guessed the stroke order right) find it. Huge advantage. Huge. So huge it's worth the price.
The Pretty Good Apps
Japanese LS Touch
by Jan Bogner
This app is on a short list of those that enable you to study by writing kanji with a finger or iPhone stylus. I'm attracted to this study method because one of the best Japanese study apps I've ever owned utilized this approach--King Kanji for the old-school Windows mobile pocket PC platform (e.g. iPaq). Japanese LS unfortunately suffers from a fatal flaw. Although it's teaching you words (not single kanji characters), it only tests 1 character on the screen at once, which really interrupts my study groove. I find studying full words far more effective than single characters, and this app defeats that benefit by forcing you to pause after each character and go to the next screen.
Japanese My Way
Another app on a short list that tests kanji handwriting is JMW. Like Japanese LS, this one only allows you to write one character of a word at a time on the screen. I suppose what King Kanji achieved on stylus-based Windows mobile isn't easily implemented on finger-based iPhone. A cool feature is how it can give you hints (like what radicals are in the kanji); but I find navigating the app's convoluted menus rather confusing. Not bad, but not one of my favs. It might be cool if there was a handwriting app like this that required you to use a stylus. That way you might be able to study whole words at once.
by Unknown Genius Software
KanjiBox is a well-built flashcard-type app with optional add-on kanji writing features, but I just find Japanese Sensei Deluxe better. Lacking features like engaging sample sentences, studying with this app gets a bit dull after a while. Plus, how many flashcard apps do you really need? This app does get better and better after each update, so while it may not yet be my top fav, it certainly deserves an honorable mention.
The Worst Apps
by ThinkMac Software
This app is so frustrating to use it makes me want to throw my iPhone out the window. Maybe I'm not a typical student of Japanese, but I'm not the type of person to sit down and study single kanji characters along with all their pronunciations. That approach is so dry and monotonous, it leeches any and all fun out of Japanese for me. If you like studying in the most unimaginative possible way, then this app is for you.
MyWords - Learn Japanese Vocabulary
by Innovative Learning, LLC
Here are some words, now let's test you! Yeah, good luck with that. This app taught me 1 thing--I wasted my money.
The Best iPhone Apps for Studying Japanese - Part 2