GIMP the Free and Open Source, cross-platform image editor available for GNU/Linux, OS X, Windows and more. GIMP provides the tools needed for high quality image manipulation.
Open source software GNU Manifesto turned 30 years on spring. Also GIMP celebrates round years: 20 Years of GIMP. November 21st 1995, few days over 20 years ago today, Peter Mattis announced the availability of the “General Image Manipulation Program” on Usenet (later “GNU Image Manipulation Program”). Over the years, GIMP amassed a huge amount of new features designed for all kinds of users and practical applications: general image editing, retouching and color grading, digital painting, graphic design, science imaging, and so on.
I used to use commercial image editing programs (for example PaintShop Pro) for my image editing needs (both for web and press publications). Sometimes many years ago I started using GIMP, and I have for many years used GIMP as my main image editing tool when making images for ePanorama.net. It can do all the normal image manipulation needed well.