GdkRgb is a rewrite of the image rendering subsystem of Gtk+. Advantages over plain Gtk+ 1.0.x include higher speed, very smooth and pretty dithered modes, and support for more displays and visuals. It is currently checked into development versions of Gtk+ (and used in the development tree of the Gimp), but is also packaged separately for application authors who want to maintain Gtk 1.0.x compatibility. The programming interface is quite simple.
Geist is an object-based image editor, designed to be used in conjunction with the GIMP. While the GIMP specializes in pixel editing, geist deals with objects. Geist's specialties are antialiased truetype fonts and a full RGBA colorspace with transparent objects blended quickly in realtime. Supported objects are lines, text (with wordwrapping and font styles), rectangles, images (zoomed or scaled with or without antialiasing), and polygons. Geist saves documents in XML, and can export to all image formats supported by imlib2.
fsv, the 3D File System Visualizer, allows you to view a collection of directories and files as three-dimensional geometry. It represents all or part of a filesystem as a collection of blocks of varying sizes, each labeled with a filename, and arranged in a manner consistent with the original directory structure. fsv can visualize any arbitrarily large collection of files, limited only by memory and hardware constraints. Program features include an integrated 2D interface, intelligent camera handling, and extensive use of animation. fsv requires OpenGL.