What are some alternatives?
OpenX - Ad technology platform available as a hosted service or as an open source download.
VertaMedia - VertaMedia is a Supply-Side Platform designed to meet the demand for efficient ad serving technology and high yield optimization.
AdRoll - AdRoll is a leader in retargeting display advertising. Draw the right people with the right strategies.
Epom Ad Server - An ad serving solution for publishers, advertisers, ad and affiliate networks
Atlas by Facebook - Atlas by Facebook is an ad serving platform that also offers tools for marketers to serve, manage, track, and measure their campaigns.
Google Marketing Platform - Google's unified and improved marketing and analytics tools.