SVGpage is an application that will render PNG images as SVG files or convert an SVG file to a PNG image. It uses an internal version of Autotrace. This is not a straight conversion to SVG (as there really is no such converter) but it does a fairly literal job with simple shapes, and renders a "painterly" effect for more photographic-style images.
Multicrush is a wrapper around pngcrush that distributes the work of brute-force compressing a single image over several pngcrush processes. This gets you a slightly less than a linear speedup, caused by different compression methods having slightly different durations. For example, the author has measured a speedup of 1.92 on a 2-core Intel T5300, and 3.86 on a 4-core Intel Q6600. The only requirements are a copy of pngcrush and at least Python 2.4. If you have version 2.6 or higher, multicrush can automatically detect how many CPUs to use.