Grafi is right in that Lowmax is a premade model / rig - though I doubt there is anything to stop you from having Lowmax drive your own model. One slight problem with that though, is Lowmax may be quite difficult to adapt to the dimensions of your model (I've never tried it myself)
As for CS... well it certainy has it's uses. But I think it really comes into it's own when you start using the CS Workbench and Track editor (so you can import preanimated clips or motion capture data to your bipeds) In truth I never really took it that far as it is a little difficult to get to grips with and at the time it wasn't necessary for me to use it in that way. I did use biped a number of times just as a rig in and of itself... It was useful, but I found it to be fairly awkward to work with and after a time went back to making my own.
As for CAT - I don't know a great deal about it - I thought it was just to create walkcycles
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