Ask HN: Creating Niche Web/Mobile Ad Network

I've identified an opportunity in creating an ad network for a niche market.

I have the connections with both advertisers and content publishers (blogs, mobile apps, etc) to really try and make a go of it.

What tools are there to manage such a network? Ideally, I'd be looking for a solution that allows me to sell ads within our network, and have content publishers easily display those ads.

Any help would be hugely appreciated.