The company originally behind the Windows NT Terminal Server idea. They have created quite a few products for use in large enterprise environments, including their most famous one called Citrix Metaframe. What Metaframe allows you to do is to remotely log on to a Windows NT Server (or UNIX, but the innovation is not as grand as on UNIX) and start a remote session through a window with the Citrix ICA Client. It's a really great applicaiton for deploying huge amounts of Windows desktops immediately.

The application works like this: you have a window, and the server sends bitmap updates to that window, while you send mouse movements and mouse clicks back. Seeing your Windows desktop on your computer, without the aid of emulation products such as VMWare, is quite amazing. Products have come before it which accomplish this task, such as VNC (by AT&T research), and PCAnywhere, now by Symmantec. The problem with those is that it did not create an entirely other session on the Windows NT machine using Windows NT native services, but rather it just sent desktop screenshots to the respective client. This solution somewhat breaks the NT Workstation / Domain paradigm, however the results are fantastic. UNIX also has a MetaFrame, except that they have had X Windows remote sessions for a while. The Windows desktop based experience is greatly enhanced by this application. This is one of Windows' " Killer App"

Microsoft bought parts of the Citrix solution, did their own custom spin on it, and created Windows Terminal Server Edition of Windows NT4. It is now bundled with Windows 2000.