Gitscout - A beautiful Github Issues experience for macOS
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
GitHub Reader - A quick way to browse GitHub issues and pull requests.
Nifty - Manage projects, work, and communications in one place.
Codetree - You can manage your entire development process through GitHub.
Jira - The #1 software development tool used by agile teams. Jira Software is built for every member of your software team to plan, track, and release great software.