Inkscape is an open source graphics tool similar to Illustrator and CorelDraw. Check out this example of a web comic who makes use of it along with the git repository to create video projects.
I ran across this post on boingboing.net, "Webcomic artists uses version control software to produce automated "making of" videos of his workflow," and thought it was pretty cool. It also points out some of the open source web design programs and tools that are out there.
The video below is an example of how web comic author Mark V uses the git repository to help him create "making of" videos for his strip, Electric Puppet Theater, by playing the git repository through ffmpeg, an audio/video converter and streaming solution.
Mark V also uses the open source program Inkscape to actually draw his comic strip:
An Open Source vector graphics editor, with capabilities similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format.
Inkscape supports many advanced SVG features (markers, clones, alpha blending, etc.) and great care is taken in designing a streamlined interface. It is very easy to edit nodes, perform complex path operations, trace bitmaps and much more. We also aim to maintain a thriving user and developer community by using open, community-oriented development.
The current stable version of Inkscape is 0.48.2 and can be downloaded here. There are versions for both Windows and Mac, if you want to try it out. If you have tried Inkscape, share your experience below and feel free to recommend other open source tools that you use.