Vtwm (the Virtual Tabbed Window Manager) is an X window manager that was developed from the twm codebase. The first release was in 1990, and it is very much an "old school" window manager. It added features like xpm icons, autoraising of windows, and a virtual desktop; the latter feature is from where the program takes its name. Later additions include playing sounds in response to window manager events, and Motif-style window decorations in place of the "flat," 2D titlebars commonly associated with twm.
Vtwm was one of the first window managers to have an icon manager, a box of click able windows which mapped to the application windows currently on the desktop. Clicking the entry in the icon manager iconizes/deiconizes the associated application. This behavior is common today in taskbars in many operating systems.
Other features of twm, including shaped window titlebars, are faithfully incorporated into vtwm.
The focus of vtwm is to maintain simplicity and compatibility. It is believed to still work under X Window System revision 4, and can be compiled and run with no dependencies beyond the standard X libraries.