Acquia , a Boston-based commercial open source software company that provides a set of tools and network services for the Drupal social publishing system, has raised $8.5 million in third-round funding. The financing comes from existing investors North Bridge Venture Partners and Sigma Partners together with Acquia CEO Tom Erickson . The Series C round brings the company's total of capital raised to $23.5 million and comes at a time when Acquia is experiencing massive growth in terms of customers and partners.