Gimp User Filter is a work-alike to Adobe's Filter Factory. It is a generic image processing plug-in that can be used to create new filters for The GIMP without having to go through the process of learning about The GIMP's SDK. Many freely available filters that have been created for Filter Factory can also be used with this plug-in.
Arachne is program that implements Avidan and Shamir's seam carving technique for content-aware image resizing. It allows realtime, fluid image resizing using this fascinating technique. Seam carving works by removing the "boring bits" from an image, so it can change the aspect ratio of many images without changing the shape of the objects inside.
SVGSlice is a simple tool which generates chopped up images from Inkscape SVG drawings. To figure out where to cut, SVGSlice can use Inkscape's built in guides (for simpler, grid-like cuts), or it can use a specially named "slices" layer that contains rectangles that mark areas to slice. Demo files showing both approaches are included.
Seg3D is a volume editing and processing tool that combines a flexible manual segmentation interface with powerful higher-dimensional image processing and segmentation algorithms from the Insight Toolkit. DICOM, VFF, META, NRRD, and many other volume formats are supported. Users can explore and label image volumes using configurable, orthogonal slice view windows and 3D volume rendering.
Flowpaint is a next generation paint program that focuses on usability and power. It's cross platform and supports pressure sensitive graphics tablets. Planned features for future versions include user-editable procedural brushes, brushes created from pictures, layers with arbitrary data channels, infinite and wrapping canvas layouts, parametrized picture templates, and built-in support for downloading and sharing new brushes and templates.