The packaging project creates the distribution artifacts: a war file, a zip file and related configuration files. The Alfresco Content Services version is determined by the packaging project, which pulls in the dependencies, as required.
The library versions have had to be advanced to 6.0 and above in order to clearly put them on an independent build and release cycle. There will probably be several minor library releases between each acs-community-packaging release.
The code was imported from Subversion with history, so we believe that these various git repositories contain nearly the entire history of Alfresco Community Edition. The SVN repository will stick around for a while so it can be used as a reference, and we are evaluating if it will be needed in the long term.
We hope this makes it easier for people to submit pull requests. If you would like to contribute, please read the contribution guide first: Submitting Contributions. Each of these repositories has a link to that document in the CONTRIBUTING.md file. You can learn more about project governance on the page Project Overview: Repository. All of this code shares the LGPL license.