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.
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.
ArahPaint4 is a textile-oriented paint program, mainly for jacquard. It is a simple paint program for raster palette images. It has good tools for drawing images in repetition, support for handling palette images (color reduction, substitution, protected, transparent colors), contour tools, layer support, unlimited undo/redo, support for drawing in aspect ratio (pixels need not be square), a two level grid, and a coordinates display. It is simple, stable, fast, and works well on large images (>8000x8000).
CinePaint is a deep paint image retouching tool that supports higher color fidelity than ordinary painting tools. CinePaint is used to retouch feature films and for professional photography. CinePaint opens high fidelity image file formats such as DPX, 16-bit TIFF, and OpenEXR, and conventional formats like JPEG and PNG. It has a flipbook for movie playback of image sequences in RAM. It supports 8-bit, 16-bit, and 32-bit color channels, HDR, and CMS.
F-Spot is a personal photo management application for the GNOME desktop. It simplifies digital photography by providing intuitive tools to help you share, touch-up, find, and organize your images. These tools include editing, color adjustments, tags, Photo CD creation, and exporting for upload.
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.
FrAid (Fr[actal] Aid) is a programming language that is appropriate for mathematical computations, visualization, batch processing, and more. It features both a standalone application that provides a programming environment for the language and a system for integrating the language with Java. The Java interface allows mathematical equations and formulas to be used with Java code, making it easier to process numerical computations, symbolic computations, imaging, CAD, and more.
GIMP is the GNU Image Manipulation Program. It is a freely distributed piece of software suitable for such tasks as photo retouching, image composition and image authoring. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, a image format converter, etc.