I've been slowly wading into App Store development recently, and while I've found Apple to be extremely supportive developers on the Mac, it hasn't released any development tools for iOS ("Xcode for iPad" is one of those mythical creatures that developers will tell you they want only after a couple rounds of drinks). This realization drew me to Codify, now named Codea, an iPad app that allows developers to write and even run XML code on the iPad.
Unfortunately, the biggest drawback with Codea was that you couldn't run that code anywhere else. The best you could do was copy the
