Is there a open source software that enables you to start your own ad network? I see there are many ad networks starting but i don’t think they all start from scratch an build their own servers etc. is there some software available?
Also the big networks do sell their inventory to other providers (and adspace vice versa) as well, not sure if this is completely automated. You will not find a (reasonibly priced) turnkey solution for that but most of the people do actually invest time (or effort) to build something to make money out of it 
You also will find a lot of scam, looking for the fast money, building such a site, getting inventory sell them expensive and such things - we’ve seen this happen with all types of software/websites/services
just use the opensource server and serve mobpartner ad campaigns. or make your own ads, you can also get the links of the interstitial ads from revmob or startapp and serve those as well.