How to set up a "public" calendar?

[Thomas Kleindienst]

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Dear list,

we've got a Kolab instance running for some weeks now.
So far it works fine, yet after a while we had the idea of setting up some sort 
of "public" calendar where a group of users gets read and write access to...

Does Kolab provide this kind of functionality (or something different which 
helps us to get a "public" calendar)?

I know, that Kontact is able to display any ics calendar e.g. from a file over 
webdav... but this is not exactly the functionality we have in mind; also 
we're looking for a solution with Roundcube...

Thomas