App Composer is a little tool that lets you package Mac applications for the Mac App Store with little hassle. We plan on updating it to potentially support more features and platforms. Comes with an update system.
App Composer serves 2 purposes: it's an easy GUI method for packaging fully signed and App-Store ready GM4Mac apps, and it's also a very fast way of packaging apps, saving developers time that would otherwise be lost typing a string of commands in the OS X Terminal. It comes with its own built-in update system to support any future feature-updates I may feel like adding.