Inkscape

Inkscape is a vector graphics editor, with capabilities similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format. It 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.
It imports various formats Postscript, EPS, JPEG, PNG et TIFF.
It exports in PNG and various other vectorial standards.