GIMP, the GNU Image Manipulation Program, is a long-standing and hugely respected open source graphics program, and many readers probably already use it. Originally created at U.C. Berkeley its interface and feature set run neck-and-neck with expensive proprietary alternatives such as Photoshop, and it has a thriving community of developers and plug-in creators. The GIMP site has many useful resources for the application, and there are also a lot of other places to visit for turning yourself into a power user of this excellent cross-platform application that always leaves new users bewildered that it is free. Here are six good choices.