I've been looking around to find software (free) for doing symbolic calculations of tensors (Riemann-Einstein-Ricci etc.) and found that there indeed exists some software (see

http://math.ucr.edu/home/baez/RelWWW/software.html ) on the net, but these are usually based on the Mathematica program, which I don't have (I switched a long time ago to the more user-friendly MathCad program). So, does anyone know of a downloadable program which does not require Mathematica ?