Computer artists have, since the invention of the personal computer, reinvented different forms of artistic expression.

To create computer graphics there are a huge number of programs from commercial and noncommercial sources:

CorelDraw (vector based)
Photoshop (raster based)
GIMP (raster based)

The word processor Microsoft Word comes with a set of basic vector graphics tools that can be used to make simple diagrams to spice up a wikipedia article. See How to draw a diagram with Microsoft Word for a tutorial. There is also ASCII art.