The Tcl Windows API (TWAPI) extension provides Tcl bindings to over 500 functions in the Windows API.
The extension provides access to the Windows API at two levels. A direct interface to the supported Windows API is provided where the Tcl commands directly map to Windows functions as described in Microsoft Windows SDK. The recommended interface is a higher level interface that is more convenient, powerful and much easier to use than the raw Windows API.
In combination with the built-in facilities in Tcl, TWAPI makes it possible to write a wide variety of Windows applications ranging from desktop applications to web servers running as Windows services. See Windows Inspection Tool Set for an example of Tcl/TWAPI based application.
TWAPI is open source and hosted on Sourceforge.