Does anyone know a good rewriter/paraphraser software or website?

That would undoubtedly be http://www.myrewriter.com. It is the best free web-based paraphrasing application I have come across so far. I have investigated and compared more than a dozen of applications in this category and myrewriter easily stands out amongst them. The best thing is the developing team are improving their system everyday, so it is best to check out how sophisticated the system is now for yourself.