  Effective use of parallel and distributed computing in science depends upon
multiple interdependent entities and activities that form an ecosystem. Active
engagement between application users and technology catalysts is a crucial
activity that forms an integral part of this ecosystem. Technology catalysts
play a crucial role benefiting communities beyond a single user group. An
effective user-engagement, use and reuse of tools and techniques has a broad
impact on software sustainability. From our experience, we sketch a life-cycle
for user-engagement activity in scientific computational environment and posit
that application level reusability promotes software sustainability. We
describe our experience in engaging two user groups from different scientific
domains reusing a common software and configuration on different computational
infrastructures.
