For some teams, all project management is done inside GitHub - which is a great choice. GitHub issues are just superior to e-mail, Basecamp or tiny little boxes in Trello.
If you spend hours every week in GitHub, you might start to grow weary of using their web UI all the time.
Ship is an excellent native application, basically an Apple Mail to your GitHub issues. If you are a person that can appreciate native application for its responsiveness, you will enjoy Ship.
Why we love it: You can work with your GitHub issues much faster than using web UI. Minutes saved every day will add up.