Rob Eisenberg provides an impressive list of features in Caliburn, a fully-baked, reusable framework for developing not only composite WPF Applications but applications of any size and complexity.
You can read the entire list of Caliburn features here.
Rob describes Caliburn with respect to Prism as
"In short, Caliburn is geared towards solving many of the same types of problems that Prism does. Prism's primary focus is on Composite Applications. Caliburn covers these scenarios, but also has a number of features designed to make general WPF development easier - regardless of the size or complexity of the project you are building."
If you are building WPF Applications, you will definitely want to check out Caliburn.