Gitscout - A beautiful Github Issues experience for macOS
16bugs - 16bugs is an all-in-one bug tracking software that makes it easier for you to manage all sorts of bugs in performance with the simple interface; ultimately, you will be more productive for sure.
GitHub Reader - A quick way to browse GitHub issues and pull requests.
Bugify - Bugify is a simple PHP issue tracker, designed to offer powerful bug tracking capabilities in an easy to use system.
Codetree - You can manage your entire development process through GitHub.
jtrac - JTrac is an open source and highly customizable issue-tracking web-application written in Java.