Recommend Fave PHP Webmail / Calendar App?

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I have a friend interested in a Linux PHP intranet web app for webmail,
calendaring, and departmental websites, all tied into a single-signon.

If it comes with features such as discussion areas, public folders,
web-based file storage, live chat (via Shockwave or Java applet, I
guess), or anything else -- that would be perks we'd like to know

I'm sure there are several products like this that are PHP-based and
are easily found with Google, but I wanted to get feedback from you on
what you happen to like.

I'm only interested in recommending PHP-based ones to my friend. I
guess I'm a bigot that way. If it is Python, Perl, CGI/BIN, or
otherwise, we're not really that interested.

Also, the backend database it uses is a big concern, so let me know
what it requires on the backend, such as PostgreSQL (preferrable to
me), MySQL (second-most preferrable), or other database.

Thanks! :)

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