The Command Bar Menu (CBM) is a part of FutureOS. It provides an user-interface for own programs. You can use pull-down menues to select functions. Windows aren't used, because the CPC-screen is little enough. CBM is not part of the core OS itself. The source code is available and it's possible to use CBM for FutureOS programs. Examples are the MP3-Player and the Sprite Konverter GMSK for FutureOS which use CBM.
Web link: http://groups.yahoo.com/group/FutureOS/files/Source%20Codes/