This article made me chuckle-- Stuart Frisby of Thirty Six Degrees wrote a short piece about five Mac OS X tools not that he'd like to see on the iPhone, but that he'd like to see in Analog Life (or Analogue Life, in his case).
The Finder function is an old favorite-- it really would be great to find your keys via a Spotlight-like interface. But Disk Utility in real life would be a nice bonus as well; a quick Restore right after I'd said something inappropriate to a lady friend would be a lifesaver. But the best would be Uno-- every car could be a Porsche, everyone could be beautiful all the time, and even fast food could taste like steak.
Five tools doesn't seem like enough-- if you could put a Mac OS X app to work in your real life, what would you choose?