Also it depends what you want to know, GT had bikes form entry level up to high end in steel, aluminium or titanium as well as thermoplastic.
There was the Tech shop stuff that was made (mostly) in house in the US, thats psyclone, zaskar, xizang as well as RTS/LTS 1,2,team.
Then you had nice tawanese made frames that were depending on year steel or aluminium like bravado's and avalanches, karakorums. Then a slew of nice bikes like richter, pantera, timberland...etc etc.
As per ever manufacturer, they changed tubesets and groupsets and parts to hit pricepints.
There are a lot of models too much to easily explain.