Free ebook, Creating Mobile Apps with Xamarin.Forms, Preview Edition, is about writing applications for Xamarin.Forms, the new mobile development platform for iOS, Android, and Windows Phone unveiled by Xamarin in May 2014. Xamarin.Forms lets you write shared user-interface code in C# and XAML (the eXtensible Application Markup Language) that maps to native controls on these three platforms.
This free ebook (PDF and Mobi) can be downloaded HERE.
This ebook is a Preview Edition because it's not complete. It has only six chapters.
Source: MSDN Blogs > Microsoft Press > Free ebook: Creating Mobile Apps with Xamarin.Forms, Preview Edition