Integrated email, calendar, documents, VoIP - "Over the air" sync to mobile devices - Microsoft Outlook, Apple, and Linux desktop compatibility - Effortless administration
Basic service is free and lets you create up to 2 forums and 2 sub forums. You also get 100MB for file attachments (like pictures uploaded by users). You can also pay $25 to $75 a month for more storage space and the ability to create and manage more forums.
A. Kittur, and R. Kraut. CSCW '10: Proceedings of the 2010 ACM conference on Computer supported cooperative work, page 215--224. New York, NY, USA, ACM, (2010)
O. Arazy, and O. Nov. CSCW '10: Proceedings of the 2010 ACM conference on Computer supported cooperative work, page 233--236. New York, NY, USA, ACM, (2010)