What are some alternatives?
When comparing PubMatic and Google Ad Manager, you can also consider the following products
OpenX - Ad technology platform available as a hosted service or as an open source download.
AerServ - AerServ offers monetization solution for mobile publishers.
AdSense - Earn money with website monetization from Google AdSense. We'll optimize your ad sizes to give them more chance to be seen and clicked.
ONE by AOL - Ad Serving and Supply Side Platform (SSP)
Smart AdServer - The only fully-integrated ad server for managing RTB, Mobile, Video & Web display. Best manage all your campaigns in one interface. Best local support
MoPub - MoPub is a mobile monetization platform that helps publishers drive more revenue from advertising and mobile transactions.