Anyone know's how Evernote develops their multi-platform App?
Do they just write from scratch for each platform or do they have some framework in between?
I don't know about the current version, but the past version was definitely not multi-platform. In this[1] blog post they explain how they moved from .NET and WPF (native) to C++ (also native) on Windows, in the transition from version 3.5 to version 4.