Loren Brichter: Designs on the future of iOS apps — Apple News, Tips and Reviews

He built his own version of the user interface framework, the software that sits right above the graphics processor on an iOS device. Apple creates that for developers — it was completely unnecessary for him to do this. But this is the kind of thing he considers “fun.”
“It’s insane,” he admitted. “But I wanted to experiment with different ways of driving graphics … Apple’s [UIKit] is the best, but I wanted to try.” The experiment was a resounding success — and now has a million guinea pigs testing his code via Letterpress. And, he said, “there have been zero issues” with what he built.

I'm a bit jealous.