Direct N-body computer simulations of the evolution of star clusters take into account all necessary - strong and soft - gravitational encounters between stars in the system. Since the times of von Hoerner and Wielen the ARI has been a place of cutting edge research in this topic. After a brief historic introduction I will introduce the current state of direct N-body simulation at the example of our mostly used code NBODY6++GPU, which is a research instrument having for our team the similar role as an observing instrument. Since a full simulation of a globular cluster over its lifetime of 12 billion years takes as many floating operations as the largest cosmological N-body runs, this is also partly a story of development of supercomputers and general purpose computing on graphics cards (GPU). The current record are models of star clusters with one million bodies (DRAGON simulations). Ideas are discussed how we will proceed in the future and why we need even more particles, e.g. to do proper modeling of nuclear star clusters. Depending on time one or two fields of current applications, done within our local and international team, will be shown and discussed: (i) evolution of black holes, their relativistic dynamics, and (ii) bound and free-floating planets in star clusters.