is a proxy X server that uses one or more other X servers as its display devices. It provides multi-head X functionality for displays that might be located on different machines.
is a nested X server, that operates as both an X client and X server.
is a X server that outputs to a window on a pre-existing “host” X display. Unlike Xnest which is an X proxy, and thus limited to the capabilities of the host X server, Xephyr is a full X server which uses the host X server window as a “framebuffer” via fast SHM XImages.
is a virtual framebuffer X server that can run on machines with no display hardware and no physical input devices. It emulates a dumb framebuffer using virtual memory.
is an X server that interacts with the MacOS X native Aqua window system
is an X server that runs under the Cygwin environment: https://x.cygwin.com