Maxima ctensor overview

I have installed Maxima (finally) and I have been playing with it a little. First part of the post is about a general explanation about what Maxima's ctensor can and can't do. Second and third part will try to explain functionality with a couple of easy examples. I have not tried neither itensor nor atensor; as I stated in the past post, their functionality is not what I need for now.
So far, and summarizing, I must admit Maxima falls short for my intentions. Truth is it's a good tool anyway and it should be easy to adapt to what I want when I had the time to go for it.

Open Source Computer Algebra Systems.

So, I started to look for computer help. As an open source freak, I have found two different packages available: Maxima and Cadabra. This post is about impressions on both of them. Not sure yet what I am going to use yet, but my hopes go to Maxima in a first approach.