Uninstalling

sudo hf-admin uninstall                     # remove the panel; websites, databases, email and DNS keep running
sudo hf-admin uninstall --purge             # also delete every hosting account and its data
sudo hf-admin uninstall --purge --packages  # also remove Nginx, Apache, PHP, MariaDB, mail and DNS software

--purge deletes every customer's websites, mailboxes and databases. It can't be undone. Copy your backups off the server first.

Before removing anything, the panel's settings and database are saved to /root/hostfog-uninstall-<date>.tar.gz.

Apps installed with the app installer (WordPress and others) can each be removed from App installer, which deletes their files and database.