Install git and git-flow with brew:
$ brew install git
$ brew install git-flow
Then install using npm:
$ npm install -g gitflow-semver
Install git from here. Make sure you choose the scary sounding option about what to add to your PATH.
Install git-flow and a shim for git-release with our installer:
> install.bat
Then install using npm:
$ npm install -g gitflow-semver
$ git release # to create a new release
$ git release --init # to initialize the repo
The actual work of creating branches etc is carried out by Git Flow. Patch releases are implemented as Git Flow hotfixes.