Free or open source software are common tools that everybody can use and customise at its convenience to create in-house applications. Using and customising free software is not sufficient to ensure that this in-house application will be maintainable at mid or long term. This paper draws lessons from our in-house project, the development of a groupware Web platform for researchers, to help defining a policy through which efficient contributions can be made to open source software so that the in-house projects may remain viable