> ...write apps: onboard, i.e. use the thing itself to build software for it.
I do this on iOS using Pythonista. It includes a basic on-device GUI design tool, hooks into various iOS built-in libraries and some useful third party Python libraries. There are even a few (admittedly trivial) apps published to the App store written in Pythonista. There's also Codea if you prefer Lua to Python. I tend to do most work in an iPad as a phone is a bit cramped for working on code.
Anyone know if thats possible, or do you still have to have an external cross-compiler/IDE to write proper apps for it?