With the release of SymphonyOS 15.0 we have introduced Kiosk Mode. This feature allows you to run any web site or web app full screen with no other interface elements to get in the way. Enabling kiosk mode is simple. Just create a file named ".kiosk" in your home directory. This file should include a single URL to your web app. Once you have saved the file simply log out and log back in.
Currently kiosk mode does not provide any direct method to exit a session. The recommended alternative is to use Ctrl+Alt+F1 to switch to a terminal, log in there and run "killall mezzo" or "service lightdm restart" either of which will end the session and bring you back to the login prompt.