ClearOS - A very good alternative for Windows Server, for free
LTSP - The Linux Terminal Server Project adds thin-client support to Linux servers.
NethServer - NethServer is an operating system for Linux enthusiasts, designed for small offices and medium...
Thinstation - Thinstation is a basic and small, yet very powerful, open source thin client operating system...
FreeIPA - FreeIPA is an integrated security information management solution combining Linux (Fedora), 389...
Nakama - Nakama is an open-source distributed social and realtime server for games and apps.