Another option that I'm currently using for a prototype at work is Java (or any JVM language) via RoboVM http://www.robovm.org http://www.robovm.org - it works

Another option that I'm currently using for a prototype at work is Java (or any JVM language) via RoboVM http://www.robovm.org http://www.robovm.org - it works similar to Xamarin so it compiles Java bytecode to LLVM to a native binary. The advantage over Xamarin is, that it uses the Apache 2 license so doesn't require hefty license fees or a subscription and you are independent. RoboVM will be released in the next couple of month in version 1.0 and it works very very well. My current prototype uses Java for all the backend / business logic (data base communication, file access, network access, threading etc.) and it communicates via a JavaScript bridge to a WebView UI layer for which I have targets for iOS (RoboVM), desktop (JavaFX), HTTP server (Jetty) and later possibly Android. All from a single Java code base which shares large amounts of code between the platforms.