Super Pipe Bird
Super Pipe Bird was an early App Store release built around one mechanic and a very small interaction surface. That simplicity was the whole point: if the timing or responsiveness was off, there was nowhere to hide. I built it in roughly a month, well before anything like today's agent tooling, which forced the scope and execution to stay tight.
It was built with a compact C++ and Box2D stack and shipped across iPhone, iPad, and Android, even though the Android version is no longer available.