Webmin, which is both free and Open Source.
Vesta Control Panel
ispmanager
Ajenti
FastPanel (free)
SPanel (free)
CyberPanel (free, but there are some security caveats)
HestiaCP (free, VestaCP fork, still supported)
ApisCP (paid, but there’s a lifetime purchase option)
Keyhelp (free)
CloudPanel (free)