I have loved Bill Waterson's Calvin and Hobbes comics ever since I was a kid and have accumulated all of the compilation books of the strips.
There have been other Calvin and Hobbes search engines before this. However they have always been quickly taken down by cease and desist letters from Andrews McMeel Universal, which owns the rights to the strips.
The search engine's creator, Michael Yingling, hopes that because the engine is for research purposes only and is not for profit could help to protect him from any possible litigation.
I recommend taking a look here while you still can. My favourite search so far has been for 'afterlife'.