Vectoraster is described as 'graphics utility for creating vector-based raster patterns and halftones based on images or gradients' and is an app in the Photos & Graphics category. There are five alternatives to Vectoraster for Mac, Windows, Online / Web-based and Linux. The best alternative is Rasterbator, which is both free and Open Source. Other great apps like Vectoraster are Posterizer (Free), Separation Studio (Paid), ZebraTRACE (Free, Open Source) and Super Vectorizer (Paid).
The Rasterbator creates huge, rasterized images from any picture. Upload an image, print the resulting multi-page half-toned pdf file and assemble the pages into extremely cool looking poster up to 20 meters in size.
Posterizer's free online rasterbator allows you to create posters larger than a standard page, using the tiled printing method. It will rasterize any image and output files that can be printed at home and reassemble to the original image.
Super Vectorizer 2 (FREE Download: http://www.svgvector.com/download/Super-Vectorizer.dmg) for Mac is a professional Mac vector tracing software that automatically converts bitmap image like JPEG, GIF and PNG to clean, scalable vector graphic of Ai, SVG, DXF and PDF on Mac.