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.
Pixel is an application for editing, retouching, manipulating, and animating RGB, CMYK, and HDR images. It was formerly known as Pixel32. It is available for Windows, Linux, Linspire, Mac OS X, BeOS, Zeta, QNX, MorphOS, FreeBSD, eComStation, OS/2, SkyOS and even old plain DOS, for both x86 and PowerPC architectures.
Allegro Sprite Editor (ASE) is a program specially designed with facilities to create animated sprites that can be used in some video game. It lets you create static images, characters with movement, textures, patterns, backgrounds, logos, color palettes, etc. It focuses on pixel editing to do pixel art. It isn't a photo retouching tool or a vector graphics editor. Mainly, it is a tool to create tiny animations pixel-by-pixel.
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.
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.
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.