Stephen Hackett wrote a great retrospective for MacStories of Aperture, one of my all-time favourite applications:
In short, Aperture was designed to let photographers import a mountain of large RAW files, sort them, perform light editing, and then export them to Finder, the web, or prints. If a user needed to carry out additional editing, Aperture included the ability to round-trip an image to Photoshop and back with just a click. If that all sounds like pro-level stuff, it was, and Aperture’s $499 price point reflected that fact.
I didn’t use Aperture until I got my mid-2007 MacBook Pro, but I remember it working pretty well for my circumstances. I knew there were plenty of satisfied Lightroom users, but its workflow just didn’t match how I edit pictures. Even today, I am a reluctant Lightroom user; I can’t tell you how much I wish Aperture were still around, with support for iCloud Photo Library. For all its faults and bugs, I always got a kick out of editing my photos in Aperture. In Lightroom, it feels like a chore.