Everyone knows and has at least once used GitHub. It is the largest code host on the planet and has over 21.4 million and many users. It is unarguably the most widely used tool by
Bitbucket's bug tracker
BitBucket is one of the largest code hosting solutions out there. Supported by Atlassian and used by millions, it uses both Git and Mercurial.
Phabricator is a collection of open source web applications that help software companies build better software.
Bugs Everywhere is a “distributed bugtracker”, designed to complement distributed revision control systems.
MantisBT is an open source issue tracker.