xneko, an X11/UNIX port of a somewhat famous cute cat chasing a mouse pointer last updated in 1993, still compiles and runs under macOS. You need Xquartz becaus

xneko, an X11/UNIX port of a somewhat famous cute cat chasing a mouse pointer last updated in 1993, still compiles and runs under macOS. You need Xquartz because xneko is an X11 program, but that’s it.