You could always use Apple iBooksAuthor -tool to publish your book quite straigth-a-forward way. It is a polished pipe to AppStore, but at the same time you are married with Apple and you must agree with fees and copyright restrictions. Here you can find some opinions and links of iBooksAuthor.
If you want authoring without marriage with Apple, Vook might be a good solution. It is not free, but you can bypass Apple and get distribution arranged otherwise. They have just teamed with Publishersweekly to offer a self-publishing platform with extras.
One canditate for authoring is cloud-based Inkling. Seems to be mostly education-oriented start-up having their own store
With InDesign assisted by eDocker Tablet Publisher you can get an app-like html5 package for tablets and also a flip-page/flash version for desktops. No fees for anyone (just buying the plug-in package), but you must have a server hosted by someone to get distribution for your book/magazine.