These repositories contain extractions of most of the bbb packages from the official ubuntu repository.
This project exists because many of the configuration files, cronjobs and shellscripts are currently not versioned and checked into the official bbb repositories. This sadly prevents people from having an easy look into issues of these parts of an bbb installation, or simply seeing the differences of these parts for each update.
See setup.md - basically its a bunch of shellscripts taped together, the most crucial part is the usage of apt-mirror.