This application will act like a gate keeper for all your applications in the environment. Just map your application along with your groups to the Portcullis application and then control your applications accessibility from a single page. If an application is marked disabled in the Portcullis app no user will be able to access the application.
This helps in situations where one particular application is ailing and throwing too many incidents/alerts and thus required to be put under maintenance without bringing the entire platform down. Post maintenance, administrators can reopen the access to the application for all the associated users with a single click.