I fundamentally disagree with the premise you can’t tinker with an iPhone. Sure, you can’t really tinker with the hardware. But you don’t need a developer account to run code on your iPhone anymore. There are IDEs of varying complexity from Workflow to Pythonista that run on your phone, and let you run your own extensions. And Mobile Safari has always been at or near the cutting edge at exposing HTML device APIs like location, accelerometer, orientation. There’s a tonne you can do in a web app. It just depends on what your definition of “tinker” is.
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