There is LOTS of info on using XML-RPC for Wordpress to be found, but believe me when I say there is no finished product that just does it out of the box.
People who have a strong grasp of PHP programming could use it to have this function done for them so they can customize it to the hilt, or if someone doesn't have any programming skills, they will have the ability to customize their own templates and post content to their Wordpress sites.
This does NOT simply pull RSS feeds, and does not SCRAPE from other sites. All the content is unique to the niche domain only. I have used it already and it works very well. I used it to create large niche directory sites that went from zero traffic to 400 unique hits a day in 3 months time.
Here is the site I've started, but why bother finishing it unless it's actually something people would want. Price suggestions are welcome too.
DO NOT BUY ANYTHING - it's not up yet.
Easy WordPress Auto Posting