You can change to a Mobile view by clicking the Style Chooser located in the bottom left corner of the JOF webpages. Essentially, it can sometimes make the webpages load a little faster if you're on a dial-up, DSL or other super slow Internet connection or WiFi, but it's at a cost of losing some of the functionality and features of the full-featuerd (Jayco Owners) view. For users on a high-speed Internet or cellular connection, though, you probably won't notice any advantage when using Mobile View.
A Mobile APP? Every forum I've ever visited is loaded by a web browser (Chrome, Firefox, Safari, IE, etc.). Mobile APPS are usually loaded by the device's operating system (iOS or Android).