A community environment using what it was once google wave and now maintained by apache (w)
Includes also calendars and forum-like capabilities with threaded view.
Pros
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All in one place.
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Free.
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record of history in discussions.
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threaded.
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open or closed groups.
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Choose license of content easily.
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chat using XMPP
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Federated, one count allows you to work in other servers.
Cons
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Wave is at first confusing