rdesktop is an open source client for Windows NT Terminal Server and Windows 2000/2003 Terminal Services, capable of natively speaking Remote Desktop Protocol (RDP) in order to present the user's NT desktop. Unlike Citrix ICA, no server extensions are required. rdesktop currently runs on most UNIX based platforms with the X Window System.

Unix (XWindow in general) had a similar feature for a long time (read XDMCP-HOWTO)/

See also