Inkscape is an Open Source vector graphics editor, with capabilities
similar to Illustrator, Freehand, CorelDraw, or Xara X using the W3C
standard Scalable Vector Graphics (SVG) file format.  Supported SVG
features include shapes, paths, text, markers, clones, alpha blending,
transforms, gradients, patterns, and grouping.  Inkscape also supports
Creative Commons meta-data, node editing, layers, complex path
operations, bitmap tracing, text-on-path, flowed text, direct XML
editing, and more.  It imports formats such as JPEG, PNG, TIFF, and
others and exports PNG as well as multiple vector-based formats.

Optional dependency: potrace (for bitmap tracing functionality).