[Discuss] What's the best secure groupware package?

[dsr at randomstring.org (Dan Ritter)]

E. William Horne wrote: 
> I'm looking for an open-source encrypted groupware program that is both
> secure and easy-to-use.
> 
> It would be nice to have something that has versions for Mac, Windows, and
> Linux, but security is the most important criteria.

What functionality do you want?

What kind of confidentiality are you keeping from whom?

Is, for example, a simple encrypted-in-transit file syncing
protocol acceptable?

Do you need (and are prepared to run) a central server?

Does everyone using it trust you?

-dsr-