potrace - Open source program that transforms bitmaps into vector graphics.
Vectorizer.io - Fast and easy way to vectorize an image online
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
RasterVect - Professional raster to vector conversion program (vectorizer).
DragPotrace - A GUI for potrace using Objective-C for OS X 10.11
vectorization.eu - Free online vectorization tool that can help you turn black&white and colored images into a vector format.