What it does: There doesn't seem to be one perfect app to quickly and easily find your way around the Tokyo subway's many lines. But we did love love love the free and very simple Trains.jp. Just enter your begin and end stations and the app (which doesn't need a 3G or WiFi connection to work) tells you what lines to take, where to transfer and how much the ride will cost. If you follow this app, you really don't even need to tote around a subway map. We used this app countless times a day in Tokyo.
Name: Tokyo Teleport Plus
What it does: Oh my god this is quite possibly the best travel app we've ever used, regardless of city. For $9.99, you get a robust app that features snippets, photo galleries and excellently produced (and hosted) videos on everything you'd want to see/do/eat in Tokyo and how to do it. A very likeable girl stars in the videos, and she goes over everything from the etiquette of visiting the Meiji Jingu shrine to how to play a Pachinko machine. We learned so much, and fast. A $4.99 version of the app eliminates the videos, but really they're the magic.
Name: Real Sushi
What it does: There are many sushi cooking/game/guide apps out there, but we wanted to find one that had a good picture glossary and a reasonable pricetag. While Real Sushi doesn't have a ridiculously extensive list of rolls, it does cover the ones you'll find at a regular sushi restaurant in Japan, and the pictures are large and the syllabic pronunciation breakdown of the Japanese words helped our sushi chefs understand us each time. Also, there's a game to test your memory when you think you know them all.
Name: Japan-i presents 'Hello Japan'
What it does: This is basically an assortment of many, many articles on Japanese sites, customs, food...all written by locals. If you shake your phone, a random article will pop up, and most are great, quick reads just to prep for your trip. We recommend this app for bathroom reading, subway rides or casual browsing while watching TV.
Name: Basic Japanese for Dummies
What it does: Instead of flipping through a little language book, we tapped our way to getting by in Japanese thanks to this app. We used the restaurant and meal section most. Turn down the volume on your phone, hold it up to your ear and use the app's voice pronunciation feature to hear the words right before you attempt saying them yourself. Super helpful and easy.
[All images: screenshots from our iPhone]