Company (http://www.microsoft.com/ ) headquartered in the state of Washington, in the business of writing software primarily (not exclusively) for use on Intel hardware.
Most well known for a series of operating systems known as Microsoft Windows and an application suite known as Microsoft Office.
For a discussion of .NET and Tcl (and Perl and Python) from the Microsoft perspective, see this article in Microsoft's Technet: "Taking Advantage of Windows 2000 and the .NET Platform" [L1 ]