title: Consistent tagging across multiple projects in separate Git repositories
body: <p>I'm working on a product which relies on several different projects each hosted in its own Git repository.  When a release is made, it would be ideal for us to consistently tag every project that is involved in building the product - this includes the core code, libraries and build tools.  Is there an obvious and sensible way to tag all projects at once?</p>
  
  <p>(It may be a distraction, or might be worth noting that each project is using Maven; perhaps there are plugins for managing this.  If so, I've not found any.)</p>