Xdmcp Chooser

Some articles on xdmcp:

X Display Manager (program Type) - Local and Remote Display Management
... In the second case, the display manager works according to the XDMCP protocol ... The XDMCP protocol mandates that the X server starts autonomously and connects to the display manager ... A server can connect, using the XDMCP protocol, to a display manager running on another computer, requesting it to start the session ...