The GNU Image Manipulation Program (GIMP) is a very popular free alternative to Photoshop. However, Photoshop users have a hard time to switch to GIMP because of the difficulty to locate Photoshop’s features in the GIMP. Fortunately, the GIMPshop developed by Scott Moschella can help these Photoshop users. GIMPshop is a fork of the free/open source GIMP, which changes the layout of the user interface to mimic Adobe Photoshop. Its primary purpose is to make Photoshop users feel comfortable using GIMP. GIMPShop was originally developed for Mac OS X, but has been ported to Windows, Linux, and Solaris.
GIMPshop is a powerful Photoshop look-alike. It modifies the menu structure and adjusts the program’s terminology to closely match Photoshop’s. Though GIMPshop does not support Photoshop plugins, all GIMP’s own plugins, effects, filters, brushes, etc. are supported. If you are looking to do basic photo-retouching, or something far more sophisticated, like work in multiple layers, I think GIMPshop has the tools you need.