On September 14, 2015, the two detectors of the Laser Interferometer Gravitational wave Observatory (LIGO) reported the first detection of gravitational waves, a signal generated from the coalescence of two stellar-mass black holes. The discovery represented the beginning of an entirely new way to investigate the Universe. From the theoretical point of view, the formation and evolution of compact-object binaries are still very uncertain. One of the main issues is that most stars form in dense stellar environments, and numerical simulations of merging compact-object binaries in such crowded stellar systems are very challenging. In this work, we review the main numerical bottlenecks that hamper our knowledge on merging binaries in dense environments and we present a new GPU-accelerated N-body code, which is currently under development, called isteddas, that can overcome most of the obstacles.