ClearOS - A very good alternative for Windows Server, for free
TrueNAS Core - TrueNAS Core (formerly FreeNAS) is a storage operating system strong and robust enough to meet the needs of enterprise level businesses.
NethServer - NethServer is an operating system for Linux enthusiasts, designed for small offices and medium...
OpenMediaVault - OpenMediaVault is the next generation network attached storage (NAS) solution based on Debian Linux.
FreeIPA - FreeIPA is an integrated security information management solution combining Linux (Fedora), 389...
Amahi - Amahi is a media, home and app server software known for its easy-to-use user interface. Amahi has the best media, backup and web apps for small networks.