SongSim by Colin Morris
SongSim uses self-similarity matrices to visualize patterns of repetition in text. The cell at position (x, y) is filled in if the xth and yth words of the song are the same.
Confused? Check out the tutorial, which walks through the example of "Baa Baa Black Sheep".
Curious for more? Check out the field guide to shapes and patterns of interest you're likely to encounter in these matrices.
Want to read even more pontification on this stuff? Check out my blog post, 6 Weird Pop Songs, Visualized.