What are some alternatives?
OpenX - Ad technology platform available as a hosted service or as an open source download.
Facebook Audience Network - Facebook Audience Network is designed to help monetize your apps and websites with ads from global Facebook advertisers.
AerServ - AerServ offers monetization solution for mobile publishers.
Google AdMob - Google AdMob or just AdMob is a mobile advertising platform that offers complete advertising solutions for many mobile platforms such as iOS, Android, Windows Phone and Flash Lite etc.
ONE by AOL - Ad Serving and Supply Side Platform (SSP)
LeadBolt - LeadBolt is a mobile advertising platform for user acquisition and in-app monetization.