IIRC the MUI website hasn't been updated for years - compare the old MagicWB style screenshots to the new MorphOS/MUI ones :-o
Of course, loads of software uses MUI (search for "MUI" on Aminet - there are too many results found, and as jahc commented you'd be very hard pressed to use AmigaOS seriously without it), so any next-gen Amiga-compatible OS has to have a version. The MorphOS team are using MUI as their primary GUI, so it's very configurable. OS4 is focused on ReAction instead, so the OS4 MUI is cut-down.
OT: Does anyone know if/when ReAction can do those gradient tricks?
