The technical term is "article spinner". Mostly used by sploggers that take content from Wikipedia (or content ripped off from other sites) and run it through the spinner application before posting it to their site. It replaces various words using a built in thesaurus list, and reorders sentences a little.
The problem with the spinners is that they don't usually generate anything of any quality that makes any sense, (sploggers don't really care since they just want ad revenue and need to not get slapped by google for duplicate content) and they aren't freeware, and usually not any kind of shareware, either.
Mostly sold through bad quality ebay ads where you pay up front and get a link for downloading...and no refunds. Sometimes you might get private label resale rights along with it, meaning that if it doesn't perform to your desired expectations, the only way you can get your money back is to post the same bad quality ebay ad (included with the software) and sell it to
another sucker someone else.
There is also no guarantee that the software doesn't contain any sort of malware, either.
Therefore, I don't think you will get many recommendations of which ones to try.