[nebalee]

Xfce (Thunar, Xfce Terminal, Mousepad) also uses CTRL-PGUP/DOWN to cycle tabs, as does MATE (Caja, MATE Terminal, Pluma uses CTRL-ALT-PGUP/DOWN). Neither uses CTRL-TAB for tabs but to cycle through buttons/icons on the GUI.

As far as I can tell CTRL-TAB for tab cycling is not very wide spread. KDE uses it, but that supports CTRL-PGUP/DOWN as well.

edit: And I'm not sure why CTRL-TAB even works in KDE because the default shortcuts to cycle through tabs are CTRL-PGUP/DOWN and CTRL-[/] (tested on KDE neon).