> IIRC, earlier SAGE was also used to be part of MathRider, along with
> many more software, but it seems it is not there.
> Am I correct?
I was a member of the Sage project back in 2007 and I created
MathRider (which is now called MathPiperIDE) as an alternative to the
Sage notebook. So in 2007, Sage was the CAS that MathRider used.
However, very few people were interested in having an alternative GUI
to the Sage notebook. When I left the Sage project in 2008, I made a
fork of the Yacas CAS, called it MathPiper, and made MathPiper the CAS
that MathRider used instead of Sage.
As for the other software that you remember being in MathRider that is
not present anymore, there were a couple of button-oriented
calculators that were removed and perhaps this is the software you are