Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Vectorizer.io - Fast and easy way to vectorize an image online
SVGO - Tool for optimizing SVG files
RasterVect - Professional raster to vector conversion program (vectorizer).
SVGminify.com - Removes superfluous information reducing the size of SVG files
vectorization.eu - Free online vectorization tool that can help you turn black&white and colored images into a vector format.