From Joomla! Documentation
< Portal:Bug Squad
The Joomla! Bug Squad uses Glip for team communication, so you are encouraged to create an account there, if you have not yet. The "Bug Squad Public Discussion" channel is for Bug Squad contributors. Drop a mail to the Bug Squad, if you can't get into that channel. You will be added manually then. Additionally, you might want to subscribe to the Joomla! CMS Development Mailing list.
Joomla! uses GitHub as its code repository and the Joomla! Issue Tracker for reporting bugs.