  We describe the Einstein Toolkit, a community-driven, freely accessible
computational infrastructure intended for use in numerical relativity,
relativistic astrophysics, and other applications. The Toolkit, developed by a
collaboration involving researchers from multiple institutions around the
world, combines a core set of components needed to simulate astrophysical
objects such as black holes, compact objects, and collapsing stars, as well as
a full suite of analysis tools. The Einstein Toolkit is currently based on the
Cactus Framework for high-performance computing and the Carpet adaptive mesh
refinement driver. It implements spacetime evolution via the BSSN evolution
system and general-relativistic hydrodynamics in a finite-volume
discretization. The toolkit is under continuous development and contains many
new code components that have been publicly released for the first time and are
described in this article. We discuss the motivation behind the release of the
toolkit, the philosophy underlying its development, and the goals of the
project. A summary of the implemented numerical techniques is included, as are
results of numerical test covering a variety of sample astrophysical problems.
