A simple paint program for Mac OS X
Paintbrush is a Cocoa-based paint program for Mac OS X, similar to Microsoft Paint and MacPaint.
Reference library for supporting the Portable Network Graphics (PNG) format.
A very high quality package of printer drivers for CUPS on Linux, Macintosh OS X, and other POSIX-compliant operating systems. This project also maintains an enhanced Print plug-in for GIMP 2.x from the same code base.
FreeImage is a library project for developers who would like to support popular graphics image formats (PNG, JPEG, TIFF, BMP and others). Some highlights are: extremely simple in use, not limited to the local PC (unique FreeImageIO) and Plugin driven!
The Animated Portable Network Graphics (APNG) is an unofficial extension of the Portable Network Graphics (PNG) format. APNG patch provides APNG support to libpng.
A Java image editor
Pixelitor is a cross-platform raster graphics editor written in Java. It supports layers, layer masks, text layers, drawing, multiple undo, etc. It has more than 80 image filters and color adjustments, some of which are unique.
XPaint is a simple paint program for X, suitable for producing simple graphics. It does offer some advanced features such as image processing functions and gradient fill. XPaint was originally written by David Koblas.
All-in-one program for creating 2D scrolling games. Compile your games into stand-alone .NET executables or customizable C# source code. The IDE and framework are build on OpenTK, which wraps OpenGL, so generated games can be cross-platform.
Box is a language specifically designed to make vector graphics easy plus a integrated development environment which facilitates the use of the language by interactively showing the graphical output. Box combines the convenience of drawing figures with the mouse with the convenience of describing them with a language tailored for vector graphics.
CDG Editor is a tool that allows the user to edit the contents of a CDG file (typically extracted from a karaoke disc as mp3+g). v1.3 now supports all CD+G command types. Please note that this is not a Karaoke creation or editing tools (see some of the comments below) - it is for fixing the CDG files that you have where the text is corrupt due to a poor rip from the original CD+G disk. You have to edit individual CD+G tile commands. This tool could be used to change the lyrics of a song for example, but it would be very difficult - that's not its purpose. Thanks for the feedback though. I've installed it on several Windows 7 64bit PCs but haven't tested the installer or the app on Windows 8 yet. Let me know via the support pages if you have problems and I'll see what I can do to help.
GraphicsMagic is an open source project that distributed under the GPL. It is an image processing application, and developed/compiled with Delphi 6/7 + Graphics32.
A generative art image evolver
"Generative art" software which evolves images/textures/patterns through an iterative process of random mutation and user-selection driven evolution. If you like lava lamps, and still think the Mandelbrot set is cool, this could be the software for you.
Imaging application for GNUstep and MacOS
PRICE: a high-quality image manipulation and enhancement application, also suitable as a multi-window image viewer. For GNUstep and Mac.
Convert Netpbm programs to GIMP plug-ins
Netpbm2Gimp automatically compiles the unmodified source code of a Netpbm graphics program into a GIMP plug-in. The result looks and functions like any other GIMP plug-in although it takes much less effort to produce than a hand-coded GIMP plug-in.
A fast, unobtrusive and modern cross-platform GUI toolkit. Agar fully exploits hardware acceleration where available, but also supports simple frame-buffer interfaces. Agar is stand-alone and easily portable to new platforms and graphics systems.
A simple photo editing and printing program. Common photo editing features and image file formats are supported. Layers and pixel editing are not supported. Version 0.90 and later includes manageImages, a photo archive manager. Versions are now available for both Linux and Windows.