SVG
From Tootsville Wiki-Wiki
Scalable Vector Graphics. Our preferred form for 2D, still artwork.
Inkscape is a great tool for creating these.
cv. Adobe Flash, the format used in Res Interactive's Tootsville. SVG is an open standard.
SVG's may be converted into PNG when you know the screen resolution, or for (slight) speed boosts in many cases. For 3D they will be converted into … (??? DXF? …)