Dan Walsh takes original strips by Jim Davis and removes the title cat completely. The results are sometimes hilarious, often odd, and occasionally sad.
Here are three examples:

click to enlarge
As you can see, it can be absurd, and Jon Arbuckle can be very sad when not being mocked by his pet cat.
Davis himself is a bit of a fan, saying the idea is "inspired" and thanking Walsh for letting him see a different side to Garfield. Awesome that he is so cool about it!
At the main site, you can view the archive, read about Dan Walsh, purchase the book based on the strip or read a FAQ.