BRIC is a powerful tool for batch image processing.
Multi-Monitor Wallpaper Editor
Advanced image processing toolbox for Scilab on Unix/Linux/Mac OS
Simple drawing program for Linux
The Utah Raster Toolkit 3.0, patchlevel 2
PNG image processing
Image Editor
Bildster is an image processing library for educational purposes.
Gimphoto is GIMP modification as Photoshop alternative
GIMP plug in to adjust images for panoramatic views
Cross-platform application for digital painting
Yocto-Gumstix LP - very Low Power, Processor intensive applications
A panographic toolkit compliant with open source standards
GUI to combine photos to get deeper DOF or HDR.
Free drawing software for Windows, Mac OS X, and Linux
comic book archive manager
Interactive designer for Celtic knots