Everyone acknowledges the importance of responsible computing, but practical advice is hard to come by. Important Internet applications are ways to accomplish business processes. We investigate how they can be geared to support responsibility as illustrated via sustainability. Sustainability is not only urgent and essential but also challenging due to engagement with human and societal concerns, diverse success criteria, and extended temporal and spatial scopes. This article introduces a new framework for developing responsible Internet applications that synthesizes the perspectives of the theory of change, participatory system mapping, and computational sociotechnical systems.