I just stumbled across a very useful site:
alternativeTo.net. This is a site to help you find "alternatives to" any given software product. The page has a very clean design and a powerful interface: you can specify what platform you want -- Windows, Mac, Linux, online (web apps), iPhone, Android, Winphone, or Symbian S60 -- and then search for a product by name.
When I selected "Linux" and searched for "Photoshop" I got
20 alternatives, most of which were new to me, ordered by the number of "likes". It's no surprise that
GIMP was on top, but I'd never heard of the #2,
GimpShop, which is GIMP modified to more closely resemble Photoshop.
And, relating to my previous post -- it found twelve alternatives to "Kompare", including Meld, Diffuse, tkdiff, xxdiff, and Kdiff3.
I think I'm going to be using alternativeTo a
lot. I've added it to our links (under "Linux Application Software").