The xeyes package provides an application that displays eyes that follow the XCURSOR in an X Window System environment. Its usecase is limited and even at the time it was made, it was considered gimmicky. It got followed up by better programs that did the premise better. The last usecase it has nowadays is determining which GUI applications use Wayland or fall back to Xorg. This is because xeyes can only follow the cursor if it is found in an Xorg environment. The general Xorg server on Wayland is shared by Xwayland. So when an application is running in it, xeyes will be able to see the cursor when it hovers over said window. For Wayland apps, the cursor cannot be found at all. Thus, you can tell which apps use Wayland or not. If you are just using Xorg, this app practically has no use. If you are using Wayland and want to, for example, see progress on Wayland support for Wine, this application will show if it is using Wayland or Xorg.
Download (HTTP): https://x.org/archive/individual/app/xeyes-1.3.0.tar.xz
Install xeyes by executing the following commands:
./configure $XORG_CONFIG && make
Now as the root
user:
make install