Developed by Netline Internet Service, the free GPL version of Open-Xchange Server includes e-mail, calendar, contacts, tasks and real-time document storage.
Frank Hoberg, chief executive officer at Netline Internet Service, said more than 300,000 people have visited the download website in the first two days since the code has been made available.
The open source version of Open-Xchange runs on the major Linux operating systems - Novell's SuSE Linux, Red Hat, Red Flag, Debian - but without support and maintenance, third-party applications and connectors.
Open-Xchange allows users to share e-mail, calendar, tasks, threaded discussions and documents originating from proprietary and open source systems.
The software supports standard protocols such as the WebDAV interface (XML), LDap, iCal and HTTP. Windows connectors will be released later this year.