Google Ad Manager - Manage your online ad sales and inventory for free

Google Ad Manager is a hosted ad management solution that can help you sell, schedule, deliver, and measure all of your directly-sold and network-based inventory.

• Simple, intuitive user interface: Decrease training time and trafficking steps with simplified tagging and inventory management.
• Google serving speed and reliability
  Ensure quicker ad delivery and fewer reporting discrepancies.
• Significant cost savings - it's free!
  Pay nothing for ad serving, feature upgrades, or system maintenance.

More Info: https://www.google.com/admanager/login/en_US/index.html

Seems very interesting. Too bad you have to apply for an invitation. :/