Openads, a developer of a free, open source ad server, announced the completion of its Series B financing. The $15.5 million investment was led by Accel Partners, with participation from existing investors Index Ventures, First Round Capital, Mangrove Capital Partners, and O'Reilly AlphaTech Ventures. The company will use the funds to accelerate product development and expand its team to support its large publisher community, which is now using Openads to deliver ads daily in over 100 countries around the world. Openads lets publishers take control of their advertising, providing tools to schedule, manage, and track online campaigns. The software also supports a broad range of ad formats and advertiser types.