WinALT: a simulation system for computations with spatial fine-grain parallelism. This system is based on a formal model called Parallel Substitution Algorithm. The system combines the best features of its ancestors. It has extensible functionality and is open for user modifications and extensions. It has a wide set of tools for visualization and representation of massively parallel distributed spatial computations. Model can be described analytically (WinALT simulation language and C language extensions) and visually in the system’s GUI.