If you're not opposed to using webmail, then the horde apps and horde add-on apps will do what you want. In Kronolith - calendar - you can have your main calendar, and create shared calendars. I use a shared calendar at home to track my boys' activities. For Turba - address book, as soon as 7.1.1 hits the street, you can create shared address books, by doing [config setprop horde SharedAddressBooks enabled ; signal-event email-update]. In nag - tasks, you can created shared task lists, and in mnemo - notes, shared notepads. If you use trean - bookmark manager, shared bookmarks.
HTH,
John Bennett