The GIMP

Read more about how the GIMP changes lives. Also see what Quartic has to say about how GIMP should be spelled.

Documentation

Writing a GIMP Plug-in: A tutorial of sorts on programming plug-ins for GIMP 1.x. If you want to get on board writing GIMP-related code, here's the place to start.

Adaptive Contrast Enhancement (ACE): The basic "Stretch Contrast" operation takes in the whole image at once, and if there is a white pixel anywhere in the image and a black pixel anywhere in the image, it figures the contrast is already as good as can be. But Adaptive Contrast Enhancement works to increase the contrast locally, and brings out details that most wide-sweeping contrast-enhancements pass over.
Antialias: The problem: When you look closely, diagonal lines in your image look blocky, with "staircase" edges. The solution to this problem (other than going out and buying a video system that doesn't use square pixels) is to blur the colors along the stair-steps a little, to soften the jagged edges. This is done without blurring any straight edges.
Maze: Draws mazes. Two styles available, and can optionally draw tileable mazes for use as wallpaper.
Refract: As if you were looking at your image through a lens. The shape of the lens is made from a greyscale heightmap, and you can change the material to be glass, water, or anything else.

These are things that I hacked on at one time or another and then left in a pile in the corner. I'm not sure which ones remain useful or functional.

I convinced Adam Moss's Superzoom plug-in (from GIMP 0.54) to go in v1.x. A snapshot of the source code is here.
gimpdock.tgz is a toy I cooked up a while back. (Quack!) It's sort of a panel for plug-ins.
I almost forgot about the janitor extension. It helps you clean up if you make a mess with lost images while writing scripts, etc.
filename.scm is a little script that will change an image's filename without saving it, so you can rename "Untitled 22" to "Bumpmap_of_Freds_Face" or something.