OPUS 4 is an open source software under the GNU General Public Licence for the operation of intitutional document servers and repositories. OPUS is an acronym for Online Publikationsverbund University Stuttgart. It was originally developed at the university library in Stuttgart at the end of the 90's. OPUS 4 is a complete redevelopment that was created as part of a DFG (Deutsche Forschungsgemeinschaft) project between 2008 and 2010. Since then the development has been continued at KOBV (Kooperativer Bibliotheksverbund Berlin-Brandenburg) mostly.
In 2015 the development was moved to GitHub in order to better support collaboration in the continued development efforts. The first OPUS 4 version developed at GitHub is 4.5. Starting with this version OPUS 4 should be installed using Git, since this will make updates for bug fixes and new features easier. More information can be found online.
The current version of OPUS is 4.5. It is available using the 4.5 tag and on the master branch. The master branch will be updated for releases or if urgent bugs have been fixed.
Documentation : Information on setting up a repository, for users and administrators.
Developers : Information for developers.
The last non-Git release of OPUS 4 is Version 4.4.5 and can be downloaded from the OPUS 4 Homepage as a tarball. The documentation for this version can be found there as well. Version 4.4.5 can be installed without Git. It is recommended to use the GitHub version of OPUS 4 for setting up new repositories. However if you are looking at migrating an existing OPUS 3 repository to OPUS 4 using this version would currently be a necessary step since there is at the moment no working migration script for the Git version.