I stumbled upon ownCloud last night and immediately had to set it up. The project is amazing, and the stuff that works, right now, is going to make you want to set it up.
Out of the box, it offers:
- File-sharing (similar to DropBox or UbuntuOne)
- Music-streaming (I think it incorporates ampache)
- Contact syncing (via CardDAV)
- Calendaring (via CalDAV)
That is just the functionality that is turned on, there are some other plugins, like providing webfinger IDs to users, as well as an OpenID stack.
Development is active on it, so it is only going to get better. I am going to play with it a bit more before getting into specifics, but you can install it yourself. More to come.