Tools

Screenshot of an application window showing a pattern of colored lines on a black background. At the bottom is a text box with a line of code presumably used to generate the image.
Tipsy Turtle, a turtle graphics program for making banners and logos.
Screenshot of an application showing a futuristic aircraft rendered in wireframe 3D, with a chalkboard-like effect.
WireView 3D, a simple previewer for 3D models in STL or OBJ format.

ASCII Mapper, a map editor for tile-based games using ASCII characters
(Screenshot depicting the 3D model of a futuristic aircraft rendered as wireframe.)
Stereo Imagination, a Python programming toolkit for generating and manipulating 3D geometry
VoxelDesc, a voxel editor driven by a command line, with 2.5D graphics and powerful scripting

Articles

(More graphics articles are on the wiki.)

Links

Color palettes

Tools and round-ups

Resource collections

Knowledge bases

2D art tutorials