Overlay dock widgets over viewport.
Glass module can be installed via the FreeCAD Addon Manager.
Install path for FreeCAD modules depends on the operating system used.
Linux:
/home/user/.FreeCAD/Mod/Glass/InitGui.py
macOS:
/Users/user_name/Library/Preferences/FreeCAD/Mod/Glass/InitGui.py
Windows:
C:\Users\user_name\AppData\Roaming\FreeCAD\Mod\Glass\InitGui.py
Qt 5 (and up) enabled FreeCAD build.
Glass module will set defaults on the first run. For activating the Tree view an additional restart of FreeCAD might be needed. For toggling the overlay mode press the Q+1 key combination on the keyboard. Q+2 key combination can be used to toggle visibility.
A video on YouTube was created by OficineRobotica demonstrating configuration and customization of Glass module. It is used as the default style for Glass and it is set on the first run.
Feedback can be posted to this FreeCAD forum thread