VectorNow is described as 'raster to vector converter, that convert BMP, TIFF, GIF, JPG file into editable DWG/DXF file'. There are more than 10 alternatives to VectorNow for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and potrace. The best alternative is Inkscape, which is both free and Open Source. Other great apps like VectorNow are Adobe Illustrator (Paid), CorelDRAW Graphics Suite (Paid), Vector Magic (Paid) and potrace (Free, Open Source).
Vextractor is a professional software for converting raster images to vector (vectorizer). Vextractor converts drawings, maps and other images, including photo, logos, black-and-white illustrations from raster to vector format.
Ludigraphix is a geometry oriented vector drawing software where shapes are defined by points that can be shared with other shapes. This allow you to build complex shapes that can be manipulated in a lot of different ways.