Shibboleth supports authenticating (i.e. identifying) users of web applications, and making authorisation decisions (i.e. working out what the identified users are allowed to do).
Note that Shibboleth, like Raven, only works in a web environment with a real user driving the browser.
Shibboleth is a standard, which increases the likelihood of people adopting it, and is designed to work across groups of independent organisations (unlike Raven, which only really works within a single organisation).
The additional power of Shibboleth comes at the price of making it all much more complex under the covers.
However many users will hardly notice ...