We've been following the Mongoliad project by author Neal Stephenson ever since it was announced last May, and the iOS apps for the project have finally been released on the iOS App Store. The apps are free, but you'll remember that the project is actually a subscription-based universe of fiction, so while there are some free things to read in there, you'll have to buy a membership or a subscription if you want access to everything. You can do so from directly within the app -- it's about seven bucks for more than a novel's worth of material, so it's not a bad price at all.
If you already have a subscription, the app will let you access the content you've got from anywhere, and/or download them so you can read offline. Even if you're not a fan of Neal Stephenson (and you probably should be -- read Snow Crash, and then read The Diamond Age, because they're both terrific), the model itself is quite interesting. We've seen a few other publications decide to publish subscription content on iOS devices, but this is the first time we've seen a fiction author publish a novel as a subscription app. It's the kind of model that should really appeal to authors with the right audience -- we'll have to see what the response to The Mongoliad turns out to be.