It meows, purrs, burps and throws out a quote or two.
In order to get the full level of activity, you need to go to the Cat.app's Edit-Preferences and push the slider all the way to the right.
This program requires Mac OS 7.6.1 or higher and 3 MB RAM. This version is for Mac PPC. The authors provide a download for 68k Macs on their site.