As sustainability continues to command the attention of open technologists, we propose a discussion of models of shared infrastructure in the nonprofit open ecosystem. Fiscal sponsorship, or the extension of the U.S. 501(c)3 tax exempt status to select groups with affiliated missions, poses particular promises to open software, open hardware, and open infrastructure projects, especially those put to the service of the public interest. We explore models of fiscal sponsorship and relate specific examples from our experience as a fiscal host to a portfolio of 15 open projects.