Literature-Map is a site that gives you a diagram of authors that it thinks you might like based on the author you put in the search bar. The closer to the original author the new one is, the more closely related they are to your search author.
I did a search for Mark Twain, since I just visited the Mark Twain House in Hartford, CT this past Saturday, and got the following diagram back.
This site could be used to find authors that are similar to other authors. A good way to use this in class would be to have the students run a search for an author they just read, and then have them determine what makes the related authors more or less related to the original.