The modular Stagger code can run simulations of deep stellar atmospheres, sunspot formation, stellar chromospheres and coronae, proto-stellar disks, star formation from giant molecular clouds, and galaxy formation. First described in 1995 for model star formation, the code has evolved and handles simulations with large ranges of both spatial and temporal scales. Stagger is efficient and highly parallelizable, provides accurate magnetohydrodynamic (MHD) solvers, handles simulations with large ranges of both spatial and temporal scales, and is adaptable to many kinds of astrophysical systems.