Ask HN: Does a self service ad tool not exist?

All of the major platforms, google, bing, facebook, twitter, instagram, pinterest, reddit etc... all have a self service ad tool that (appears to be) the primary source of their revenue.

What I cannot for the life of me find, is a product or OSS that is such a tool for other products/services/companies to implement. Am I totally missing something or did every single one of these brands build their own self serve PPC system?

Note, I am not talking about ad networks where you submit your application to them and then serve ads from the network. I am talking about systems that manage sponsored or native content in the application.