The GNU Image Manipulation Program (GIMP) version 2.0 was released on the 23rd of this month. The GIMP is a freely distrubuted OpenSource program that does exactly what its title says. It is most frequently compared to the commercial program, PhotoShop, which is made by Adobe.
The GIMP is available in a number of languages and for a variety of platforms, including Windows, OSX and Linux. If you want to get a copy for yourself, follow the linkson the GIMP for Windows page.