For example:

A publisher launches a site about dogs. The publisher invites freelance writers to contribute stories about certain dog types. Instead of paying the writers for the stories up front, the publisher pays the writers a percentage of the revenue that their stories generate. Revenue is generated by pay-per-click (PPC) ads such as Google Adsense, cost per thousand (CPM) ads such as banner ads, and affiliate programs, such as the one offered by Amazon. Are there services that facilitate this arrangement?