  This paper extends the FAIR (Findable, Accessible, Interoperable, Reusable)
guidelines to provide criteria for assessing if software conforms to best
practices in open source. By adding 'USE' (User-Centered, Sustainable,
Equitable), software development can adhere to open source best practice by
incorporating user-input early on, ensuring front-end designs are accessible to
all possible stakeholders, and planning long-term sustainability alongside
software design. The FAIR-USE4OS guidelines will allow funders and researchers
to more effectively evaluate and plan open source software projects. There is
good evidence of funders increasingly mandating that all funded research
software is open source; however, even under the FAIR guidelines, this could
simply mean software released on public repositories with a Zenodo DOI. By
creating FAIR-USE software, best practice can be demonstrated from the very
beginning of the design process and the software has the greatest chance of
success by being impactful.
