Michal,
The MathTensor package is available from me. It is not a Wolfram Research package. Those interested can contact me at my sunfreeware@gmail.com address. MathTensor does all that I need for tensor analysis; honestly, I do not know in detail what other packages or functions can do. A search at the Wolfram main site or here in the Community will turn up several ways of doing tensor analysis or packages by other developers that might be available.
Steve C.