OpenGoo is an open source web office package that is designed to be an alernative to something like Google apps. Currently it has modules for text documents, presentations, task lists, e-mail (though that’s still in beta), calendars, web links and contact management.
Last month I downloaded about 8 different similar packages and tried them on my server, but OpenGoo is far and away the best open source office-style package I’ve tested. The interface is actually usable by normal human beings.
There’s a demo of the software in action here.