This is a list of notable applications that use GTK and/or Clutter for their GUI widgets. Such applications blend well with desktop environments that are GTK-based as well, such as GNOME, Cinnamon, LXDE, MATE, Pantheon, Sugar, Xfce or ROX Desktop.
Official GNOME applications
The GNOME Project, i.e. all the people involved with the development of the GNOME desktop environment, is the biggest contributor to GTK, and the GNOME Core Applications as well as the GNOME Games employ the newest GUI widgets from the cutting-edge version of GTK and demonstrates their capabilities.
Shells, user interfaces, application launchers
GNOME Shell – the desktop graphical GUI shell introduced with GNOME version 3.0
Cinnamon fork of the GNOME Shell
GNOME Panel and forks – applications launcher
Maynard, a shell for Weston by Collabora originally for the Raspberry Pi
Budgie is a distro-agnostic desktop environment
Education software
Tux Typing – typing tutor for children
DrGeo – geometry software
GCompris – educational entertainment for children (legacy version only)
Utility software
Operating system administration
Disk Usage Analyzer – Disk-usage analyzer
GNOME Disks – utility for the hard disk; partition editor, S.M.A.R.T. monitoring, formerly known as Gnome Disk Utility or palimpsest
GParted – utility for the hard disk; partition editor
Despite the immense popularity of Qt, there continues to be science software using the GUI widgets of version 2 of GTK toolkit. Whether this is going to remain that way, or whether the software will be ported to some current version of GTK (maybe GTK 4) remains to be seen.