Sustainability education and conservation have become an international imperative due to the rising cost of energy, increasing scarcity of natural resource and irresponsible environmental practices. This paper presents Makahiki, an open source serious game framework for sustainability, which implements an extensible framework for different organizations to develop sustainability games. It provides a variety of built-in games and content focused on sustainability; game mechanics such as leaderboards, points, and badges; a variety of common services such as authentication, real-time game analytics and ability to deploy to the cloud, as well as a responsive user interface for both computer and mobile devices. The successful implementation of six sustainability educational games in different organizations provides evidence regarding the ability to customize the Makahiki framework successfully to different environments. [Additional funding for this work was provided by the Hawaii Electric Company. For the complete proceedings, see ED557181.]