Rdesktop

rdesktop is an implementation of a client software for Microsoft's proprietary Remote Desktop Protocol (RDP). Rdesktop is free and open-source software, subject to the requirements of the GNU General Public License (GPL-3.0-or-later), and is available for Linux and BSD as well as for Microsoft Windows.

As of August 2013, rdesktop implements a large subset of the RDP 5 protocol. Unlike Remote Desktop Connection in modern versions of Windows, rdesktop still supports the older RDP 4.0 protocol used by Windows NT 4.0 Terminal Server Edition and Windows 2000 Server.

Feature set
RDP5 features supported:
 * Bitmap caching
 * File system, audio, serial port and printer port redirection
 * Mappings for most international keyboards
 * Stream compression and encryption
 * Automatic authentication
 * Smartcard support
 * RemoteApp like support called "seamless" mode via Seamless RDP
 * Network Level Authentication

Still unimplemented are:
 * Client redirection upon reconnect (of disconnected session)
 * Remote Assistance requests
 * USB device redirection

Support for the additional features available in RDP 5.1 and RDP 6 (including multi-head display spanning, window composition and console connection) have not yet been implemented, although some have been officially documented on MSDN.

Use
Rdesktop is commonly used on desktop ReactOS and Linux installations to connect to Microsoft Windows running Remote Desktop Services. There are many GUI clients, like tsclient, Gnome-RDP and KDE Remote Desktop Connection (KRDC), which are graphical front-ends to rdesktop. The program has also been integrated into several thin client Linux distributions like Thinkstation and the PC TSC project, as well as some thin client appliances.