Collabtive as an open source project management and collaboration solution started by Philipp Kiszka and Marcus Frohner in November 2007. The second stable release of Collabtive has been made publically available in August 2014. Collabtive is still a work in progress, lacking critical collaboration tools, like document management, videoconferencing and native mobile apps. If you are looking for a free Collabtive alternative, Bitrix24 makes a great choice.
* Please note that the information may have changed since the publication. For current prices and features please visit Bitrix24 pricing page.