I was one third of the engineering team that built the 'Grid' iPhone app (https://itunes.apple.com/us/app/grid-by-binary-thumb/id649597509). The version we developed was...more featured by Apple in the app store for several weeks. I helped with all aspects of the product from design to debugging, focusing primarily on architecture and front-end.
My hands used to bother me when using mouse/keyboard too much, so I invented a new type of text editor that would be more efficient to use with motion sensors (and other low precision input devices). It was on the front page of Hacker News, its video demo got ~15,000 hits, it was cited in research, and written about in a software periodical in China.
Since then I was one third of the engineering team at a YCombinator startup where I learned iOS development from scratch and within a few months produced an app that Apple featured in the App Store.
Then I came up with and developed a new kind of debugger (an 'abstract visual debugger'/3d data structure visualizer) which was on the front page of Hacker News again.
Then I worked for a multi-material 3D printer startup that grew out of a materials science lab at Harvard, learned web development and built a 3D print simulator for them, among other things.