Seashore is an open source image editor for Mac OS X's Cocoa framework.
It features gradients, textures and anti-aliasing for both text and brush strokes. It supports multiple layers and alpha channel editing. It is based around the GIMP's technology and uses the same native file format.
However, unlike the GIMP, Seashore only aims to serve the basic image editing needs of most computer users, not to provide a replacement for professional image editing products. Seashore was created by Mark Pazolli who, together with a handful of other developers and helpful users, still develops it to this day.