Inkscape is an open source vector graphics editor, similar to Adobe Illustrator. It is native to Linux, but Windows and MacOSX ports are available.

Its user interface is slightly laborious at times, but overall, is well designed. It supports gradients, curves, PNG export, star objects with many properties including randomisation - allowing the creation of spirographic patterns.
It uses the SVG format, and is working towards eventually supporting it entirely.
An interesting thing is that some of the documentation, the about dialog, etc are SVGs that were created with Inkscape.

The Windows version runs a bit sluggishly on my 700mhz Pentium, with 320mb of RAM. I haven't tested the native Linux version however.

Inkscape was founded by developers of Sodipodi due to differences, and is now up to version 0.39.

The URL is