With multiple similar git repositories, for example where a base repository contains a framework or base system installation and other repositories are created from that repository, it's possible to save some time when cloning down another repository by using the
reference option to git-clone:
git clone firstname.lastname@example.org/my/repo --reference another-repo
another-repo points to a local version of a repository.)
The reference here doesn't have to be the base repository itself, it could just be another variant of it. The speedup can be quite dramatic if the repositories have megabytes of shared history, from minutes to seconds.
On a related note, I'm surprised that GitHub doesn't allow for multiple renamed forks, which would be very useful in this scenario. BitBucket does support this, however. It even has a 'sync' button for pulling updates from the base into the child repositories, which is very useful, especially for those who prefer GUIs over CLIs.