Atom interferometers have demonstrated high sensitivities in measurements of accelerations, rotations and different physical constants. In this article, we present the mobile instrument GAIN (Gravimetric Atom Interferometer) which allows to utilize this potential for high-precision on-site measurements of the local gravitational acceleration. Important influences and systematics arising from both the experimental realization as well as the environment and possibilities to distinguish between them are reviewed. In addition, we give a compact overview of other established gravimeters and discuss the performance of GAIN in the context of several comparison campaigns.