GIMPshop is a modification of the free/open source GNU Image Manipulation Program (GIMP), intended to replicate the feel of Adobe Photoshop. Its primary purpose is to make users of Photoshop feel comfortable using GIMP.
It shares all GIMP's advantages, including the long feature list and customizability, while addressing some common criticisms regarding the program's interface: GIMPshop modifies the menu structure to closely match Photoshop's, adjusts the program's terminology to match Adobe's, and, in the Windows version, uses a plugin called 'Deweirdifier' to combine the application's numerous windows in a similar manner to the MDI system used by most Windows graphics packages. While GIMPshop does not support Photoshop plugins, all GIMP's own plugins, filters, brushes, etc. remain available.
Due to the changes to the interface, many Photoshop tutorials can be followed in GIMPshop unchanged, and most others can be adapted for GIMPshop users with minimal effort.
GIMPshop Download Page