TrueNAS Core - TrueNAS Core (formerly FreeNAS) is a storage operating system strong and robust enough to meet the needs of enterprise level businesses.
Webmin - Webmin is a web-based interface for system administration for Unix.
OpenMediaVault - OpenMediaVault is the next generation network attached storage (NAS) solution based on Debian Linux.
ClearOS - A very good alternative for Windows Server, for free
Unraid - Simplicity. Flexibility. Scalability. Modularity. Unraid empowers you to build the system you’ve always wanted using your preferred hardware, software, and operating systems.
cPanel - With its first-class support and rich feature set, cPanel & WHM has been the web hosting industry's most reliable, intuitive control panel since 1997.