LTSP - The Linux Terminal Server Project adds thin-client support to Linux servers.
VirtuaWin - VirtuaWin is a virtual desktop manager for the Windows operating system (Win9x/ME/NT/Win2K/XP/Win2003/Vista/Win7/Win10). A virtual desktop manager lets you organize applications over several virtual desktops (also called 'workspaces').
Thinstation - Thinstation is a basic and small, yet very powerful, open source thin client operating system...
Sysinternals Desktops - Desktops allows you to organize your applications on up to four virtual desktops.
Nakama - Nakama is an open-source distributed social and realtime server for games and apps.
9Desks - up to nine virtual desktops