In older versions of LiveProject, viewers started out as separate windows (And back then they were called monitors). From version 2.0 and forward, new viewers are created in tabs in the Main Window. It is still possible to Detach and Attach viewers however, using the Detach and Attach Main Menu options:
Select Detach from the main menu to detach the viewer to a separate window:
The detached viewer now 'floats' in its own window, and can be placed anywhere on the screen.
Select Attach on a detached viewer to re-attach it to the Main Window