[QUOTE="AD."]\nNot yet as such. Lotus Notes/Domino and Novell Groupwise are the only real\nproducts that do as much as or more than Exchange and they aren't open\nsource. Anyway I find Notes/Domino such a pain that I prefer Exchange ;) \n\nThere are a few open source calendar sharing type systems, but they are\ngenerally clunky and have limited choices for clients. The whole area has\nsuffered from a lack of standard protocols and formats, but that seems to\nbe changing these days.\n\n\n\n\nI have high hopes for this new one (although I haven't tried it yet):\n\n[URL]http://www.hula-project.org/Hula_Server[/URL]\n\nIt's not a full Exchange replacement but it should take care of the\nshared calendaring bit which is all most (not all by a long shot) \nExchange users seem to use.\n\nOnce someone writes an Outlook plugin for Hula, I would seriously consider\ndropping Exchange here. Then once that happens it should be much easier\nfor users that don't want Outlook to switch to something else. But writing\na good Outlook plugin is hard, and I don't expect a mature one for a while.\n[/QUOTE]\n\nThere was some press about the Bynari Insight groupware server a while \nago, it runs on linux, but its not free or open source.