This article studies the building of a successful open-source project for the public sector, named CommunesPlones. It proposes an original institutional arrangement to onboard different users, especially those unable to contribute in code, for them to express their needs and provide the resources needed to develop and maintain the software addressing them. It has created an open-source editor collectively owned by its users. This pooling by a trusted third party model may appear as an alternative to the classic FLOSS projects, when users have few development skills, even if the consequence is that, although the code is still open, the development is centralized by this special type of opensource editor.