This is Maximus GNOME Shell extension ported to Cinnamon.
I only changed the metadata.json file, extension works in Cinnamon without any changes.
All credits go to its original author. (See website: https://bitbucket.org/mathematicalcoffee/maximus-gnome-shell-extension/overview)
This extension hides a window's titlebar when maximized, could be great on small screens with Cinnamon Window buttons extension and a top panel.
Screenshot shows it in action, you can see GEdit with German localization and no titlebar.