There's a new tsumego book in the app store, this time by the Nihon Kiin. It offers several levels. and you can solve the first 10 of each level.

To get the full sets (for the beginner and advanced kyu there are 60 problems), you have to make an in-app purchase of 0.99$ (0.79€)

The app is pretty smooth, and although I found the price high at first, it's just 0.015$ for problem, which is a good deal for tsumego. It's compatible with iOS 4.2, so you can play in your iPod Touches 2nd gen (like mine )

There's also another app (by a korean, I can't remember the name right now), which also offers a free trial (6 levels and 30 trial problems), whereas the full version offers 300 problems per level (1800 total) for (I think) 5.99$ 4.99€ I say "I think" because there are several apps by the same developer, and although three are marked as 1-2-3 (priced 2.99), there's another one priced like this without numbers: I assume it's the full version, but who knows? If someone does, please let me know This one is only compatible with iOS 4.3 or later, and has a bug in one of the problems (ko in the edge -> application exits).

I'll add the Nihon Kiin app to my Go app review queue for whatsoniphone.com, stay tuned to the category "baduk"

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Geek of all trades, master of none: the motto for my blog mostlymaths.net

Some nice problems (i rly like micro tsumego collection) but UI is simply terrible and switching between problem lists is slow, maybe due to useless background animation.
Missing review mode, bad navigation and terrible font choice giving headache when on iPad,...
Only good thing in UI is goban movement.

I bought it but i am using it only as additional tsumego problems library for real goban. Magickbaduk, master of go, smartgo are much better for solving problems on mobile device.