ClarusX is a hack to replace the page setup dialog icons (known in the Apple community as "boring guy") found in OS X with a variety of cattle including something that's gained mini-cult status known as "Clarus the DogCow".
If there were an award for pointless apps, then ClarusX may well win it although it does bring a bit of fun to OS X. The dogcow is a bitmapped image first introduced by Apple in the shape of a dog in 1983 and later chosen for the Mac OS Print Setup dialog box. A modified version of it became the image famously known as the dogcow.
Be warned that ClarusX is what's know as a Haxie application - a term used to describe an application which makes fundamental changes to your Mac system. You may have problems removing it afterwards as a result and there is a lot of controversy as to whether it's an ethical and even legal way to develop software on the Mac. However, in this case, the developers have provided documentation about how to remove ClarusX properly.
It may be a bit pointless but if you've been there since the early days of Apple, then you might find ClarusX amusing.
