Lightroom
Jeff Schewe writes about the history of Shadowland/Lightroom, which Adobe started working on about four years ago, and Michael Reichmann wrote a good introduction to it (via John Gruber). Interestingly, Lightroom, like iTunes, doesn’t require the files to be in the library the way Aperture and iPhoto do.
Gus Mueller says that over 40% of Lightroom is written in Lua.