Scalable OGo (SOGo in short) is a groupware server built around the SOPE application server. Unlike OGo, it is focused on scalability instead of depth in functionality. The Web interface uses human-readable URLs and can be accessed according to REST Web service ideas. Notably, it requires no server side session at all. The server stores all internal data in the iCalendar format, and therefore has no data model inconsistencies with native clients. It easily connects using GroupDAV connectors.
Information regarding Project Releases and Project Resources. Note that the information here is a quote from Freecode.com page, and the downloads themselves may not be hosted on OSDN.