Free and Open Source Software (FOSS) has come to play a critical role in the global software industry. Organizations are widely adopting FOSS and interacting with open source communities, and hence organizations have a considerable interest in seeing these communities flourishing. Little research has focused on the tools used to develop that software. Given the absence of formal mandate that would appear in traditional organizations, an open question is what influences a FOSS contributor's decision to adopt a tool and how workflows get established in FOSS teams. In this paper we report on a Delphi study conducted in the Debian Project, one of the largest FOSS projects. Drawing from data collected in three phases from a panel of 21 carefully selected and well-informed participants, we identified 15 factors that affect decisions to adopt tools and relate those to existing models of innovation and diffusion. CCS Concepts• Software and its engineering → Software maintenance tools; Collaboration in software development KeywordsFree/open source software, tools, Delphi study, qualitative study