Yamaha has updated its Synth Book iOS app, which contains the AN2015 virtual analogue synth, to version 1.5. This adds 64 new voices to said synth, plus support for Inter-App Audio and Audiobus.
That's more sounds and better integration with your other iOS apps, then - the rest of the app seems to be pretty much as before. You can find out more about Yamaha's 40 years of synth design in the History section, and you'll also find news, links to Yamaha's websites and videos of current products.
The Yamaha Synth Book is available for free from the Apple App Store (opens in new tab) and compatible with the iPhone, iPad and iPod touch (it's optimised for versions 5, 6 and 6 Plus of the iPhone).