FOSolverS, a suite of free and open source solvers, is a scientific computation project created with the following design goals: 1. The product should be able to solve practical engineering problems. (It is likely to be more useful than your CFD course project from grad-school.) 2. The product should be easy to hack. (There are not many fluid dynamics expert who are also experienced C++ architect.) Currently the project consists of three major components: libfosolvers: unstructured grid data structures and procedures, grid and data IO, interface to algebraic solvers, FVM and FEM spatial schemes, condition management framework, UDF management framework. fopbc: a general-purpose, compressible, "all-Mach-range" fluid solver. The solver employs a pressure-based-coupled method which solves the pressure and momentum equations simultaneously, and solves the energy equation in a segregated way. foeuler: a general-purpose, compressible Euler equation (invisid flow) solver. The solver uses first-order Roe's scheme for spatial discretization, and BDF-Newton-Krylov method for temporal stepping.