GIMP for free/open source photo editing
Any photographer is familiar with the industry standard Adobe Photoshop. Unfortunately Photoshop is expensive and cumbersome. It would be nice to have all of that functionality, but I prefer to keep my money. And if you use Linux Adobe doesn’t make a Linux client anyway. Fortunately there is a very good and free solution. It is called GIMP (GNU Image Manipulation Program). For hard core Photoshop users GIMP is not an exact replacement, but for the rest of us GIMP does everything you can possibly imagine. Obviously there are other free tools that have much of the same functionality and are probably easier to use (Google Picasa), but this does all of that and provides you with many amazing features that you soon won’t be able to live without.
Ars has an in depth look at GIMP and its various features (the article is 10 pages long). If you have been looking for a free alternative to Photoshop this is your place.