Can we change the parent app of a module?

Yes, Admins can change the parent app of a module by clicking on the menu for the selected module in Settings > Modules page, and click on "Change parent app"

Users can also personalize the items in the main menu and customize the modules to be shown in an app. For example, if a user prefers to have "Social" module be seen under Sales app, then can do so by clicking on the "Personalize" link in main menu.