This mini-symposium aims to assemble both developers and users of open-source scientific software libraries for fluid and solid mechanics. It will encompass discussions on software design and performance, which includes topics such as data structures, the implementation of approximation methods, adaptive hp-refinement, and high-performance computing. Additionally, the mini-symposium will delve into linear solvers for large systems of equations, meshing tools, and various pre- and post-processing tools. Intended as a forum for developers, contributors, and users of open software libraries, the mini-symposium will facilitate the sharing of knowledge and experience about modern infrastructures, emerging technologies, and algorithms. It will also cover performance profiling, testing, and development. The symposium will provide insights into the process of building and managing communities of developers and users, drawing from experiences with successful and widely-used open-source codes such as FEniCS project, deal.II, MFEM, PETSc, MoFEM, and others.