John Burkardt: scientific computing source codes
PETSc: suite of data structures and methods for solving distributed linear algebra
Spack: HPC manager
OpenFOAM: most popular CFD platform at the moment
SU2: Standford’s simulation and design suite
Clawpack: conservation laws package
Free CFD codes: creamer of the book I do like CFD
OpenFVM: no longer maintained
UnstEuler2D: unstructured 2D Euler solver
FEniCS: solver for PDEs in variational form
Gridap: 100% Julia stack similar as FEniCS
deal.II: C++ library
PyFR: Python based framework for solving advection-diffusion type problems using the flux reconstruction method
FR1D: 1D linear and nonlinear advection equation solver using flux reconstruction