SVGO - Tool for optimizing SVG files
miniPaint - Online graphics editing tool use HTML5 technologies like Canvas, Offline support, Drag and Drop.
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
RealWorld Paint - RealWorld Paint is an free portable image/photo/animation editor.
Scour - SVG Optimizer / Cleaner
JugiPaint - JugiPaint is a painting software with diverse tools for various types of illustration work.