  Scientific workflows have been used almost universally across scientific
domains, and have underpinned some of the most significant discoveries of the
past several decades. Many of these workflows have high computational, storage,
and/or communication demands, and thus must execute on a wide range of
large-scale platforms, from large clouds to upcoming exascale high-performance
computing (HPC) platforms. These executions must be managed using some software
infrastructure. Due to the popularity of workflows, workflow management systems
(WMSs) have been developed to provide abstractions for creating and executing
workflows conveniently, efficiently, and portably. While these efforts are all
worthwhile, there are now hundreds of independent WMSs, many of which are
moribund. As a result, the WMS landscape is segmented and presents significant
barriers to entry due to the hundreds of seemingly comparable, yet
incompatible, systems that exist. As a result, many teams, small and large,
still elect to build their own custom workflow solution rather than adopt, or
build upon, existing WMSs. This current state of the WMS landscape negatively
impacts workflow users, developers, and researchers. The "Workflows Community
Summit" was held online on January 13, 2021. The overarching goal of the summit
was to develop a view of the state of the art and identify crucial research
challenges in the workflow community. Prior to the summit, a survey sent to
stakeholders in the workflow community (including both developers of WMSs and
users of workflows) helped to identify key challenges in this community that
were translated into 6 broad themes for the summit, each of them being the
object of a focused discussion led by a volunteer member of the community. This
report documents and organizes the wealth of information provided by the
participants before, during, and after the summit.
