As described by Lifehacker.com: "Mangle is a handy tool for formatting your Manga and comic collections for easy reading on your Kindle. It includes page sorting, downsampling, and auto rotation for fuss-free reading."
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.