git-upstream is an open source Python application that can be used to keep in sync with upstream open source projects, mainly OpenStack.

The main usecase for this tool is for people who are doing active contributions to repositories that are mirrors of OpenStack repositories, with the intention that most of those contributions will be submitted to review.openstack.org at some point.
If you are running a public cloud based on OpenStack, having local changes needed to use it in your environment, you can use git-upstream to stay up to date with the upstream master in a easier way (with respect to using raw git commands).

git-upstream provides new git subcommands to support rebasing of local-carried patches on top of upstream repositories. It provides commands to ease the use of git for who needs to integrate big upstream projects in their environment. The operations are performed using Git commands.

Documentation is available online at http://git-upstream.readthedocs.io/en/latest/