Zrythm is an interesting open-source digital audio workstation (DAW) software package. It’s been making use of the GTK toolkit but now the developers have decided to switch to Qt6 instead.
It’s really rare for a project to completely rewrite to a new toolkit. VLC in circa 2007 did it (moved to Qt - even stole their volume control widget directly from Amarok at the time). GCompris ended up as a KDE project despite originating in Gnome (along with toolkit change, but it weirdly kept the name). LXDE->LXQT also. But I don’t actually have that many examples.
It’s really rare for a project to completely rewrite to a new toolkit. VLC in circa 2007 did it (moved to Qt - even stole their volume control widget directly from Amarok at the time). GCompris ended up as a KDE project despite originating in Gnome (along with toolkit change, but it weirdly kept the name). LXDE->LXQT also. But I don’t actually have that many examples.
audacious too! though oddly enough they’ve gone back to gtk3 in recent versions alongside their qt version