This script has been moved to github and is now maintained by bill-auger in order to have a proper issue tracker - all further development and communications will take place there. Thank you for your stars and comments here!
https://github.com/bill-auger/git-branch-status/
this script is also now icluded in jwiegley's git-scripts collection but please direct comments, bug reports, and feature requests to the upstream issue tracker
What a great script! 😍 Like you guys, I added colours and columns, and an indication of whether this branch has been merged into master, but I will admit my version is somewhat convoluted.
However, if you are only interested in the _current_ branch, then perhaps you would prefer to see ahead/behind counts on your prompt.