The Concurrent Versions System (CVS), also known as the Concurrent Versioning System, originally invented and developed by Dick Grune in the 1980's implements a version control system: it keeps track of all work and all changes in a set of files, typically the implementation of a software project, and allows several (potentially widely separated) developers to collaborate. CVS has become popular in the free software and open-source worlds. CVS is released under the GNU General Public License.