ergophobe - 7:14 pm on Feb 2, 2012 (gmt 0) [edited by: ergophobe at 8:09 pm (utc) on Jul 7, 2012]
You don't say anything about budget
I believe that Adobe Contribute is designed for the type of thing you're considering, runs on Mac and Windows, and a 5-user pack can be had for $800 (unfortunately, I don't think you can mix and match, 2 Macs and 3 Windows).
Or you could go with a traditional CMS that has static export built into its guts and people would connect to the server (violates your offline criterion).
MoveableType has static and dynamic publishing modes. [movabletype.org...]
Typo3.org has a static output option: [typo3.com...] Last i tried it, I simply could not wrap my head around Typo3, so it might be a bit of a ramp up, but fans always sing about its capabilities.
[edit: your followup was posted while I was writing this, so I realize better what you mean by offline]
[edited by: ergophobe at 8:09 pm (utc) on Jul 7, 2012]