Built for Mac
This is a real Mac app. It has the keyboard shortcuts, menus, customizable toolbars, and more that you expect from a Mac app.
Built for iPhone
This is no cut down Mac port. It uses gestures and modern context menus to expose all the advance functionality it shares with the other versions.
Built for iPad
As powerful as its siblings with support for all the same keyboard shortcuts. Naturally, it supports multiple windows and side-by-side windows.