L-Galaxies is a semi-analytic simulation of galaxy evolution on a cosmological scale, running on the "merger trees" of dark matter halos generated by N-body simulations of the hierarchical formation of structures.
Thanks to its semi-analytic nature, L-Galaxies can model the evolution of millions of galaxies from very early times to the present much more efficiently than hydrodynamic simulations of comparable size. This makes L-Galaxies ideal for testing models of astrophysical processes, as well as for studying statistically significant samples of galaxies and the supermassive black holes they host.