My first post here:
Simultaneously available for Macintosh, Windows and Posix/Unix.
Progressive image update: watch it generate
Save generated images in PNG or SVG format.
Edit grammars and re-render easily.
Render very large images (as large as 100 Mega-pixels).
Can handle generated images with millions of shapes.
Carefully tuned graphics rendering
Many built-in examples
Automatic checking for updates (Mac only).
It's free, as in beer and as in speech.
Context Free Homepage