Mac OS X only: Free, open-source application Seashore is a light-weight image editor based on the GIMP.
Seashore is built using GIMP's framework and is streamlined specifically for Mac OS X. Unlike GIMP, Seashore does not require the X11 Window System. While Seashore is stripped of some of GIMP's more powerful features, it's perfect for image editing and light-weight image manipulation. Seashore is a free download for Mac OS X only.
Seashore [Sourceforge]