EinS is a package for Mathematica allowing one to perform symbolic calculations with indexed objects (e.g., tensors) with indices remaining symbols. EinS handles automatically Einstein summations, dummy indices and user defined symmetries of objects. It has an efficient simplification algorithm and various pretty printing and exporting capabilities.
Klioner, S.A. (1998): New system for indicial computation and its applications in gravitational physics. Computer Physics Communications, 115, 231-244