The appeon_workarounds.pbl has a number of useful features.  Related to creating a universal app, you would want to use the of_getclienttype ( ).  By detecting what mode the app is running on you could hide certain menu items, buttons, etc. so that a web user is accessing the features appropriate to them and mobile user is accessing appropriate features to them.  For example, you wouldn't want on Web to try to trigger the mobile APIs (e.g. camera) that PowerServer supports on iOS/Android.

Although technically possible, you really should ask yourself whether it is appropriate to go in the direction of a universal app?  In a nutshell, this will depend on your app complexity and the type of mobile devices you are targeting.  Some things for you to consider are:  

1. If your app is simple and would run on tablets not phones it is feasible to have a single app UI (designed with tablet touch in mind of course) that runs in the Web browser and on iOS/Android tablets. 
2. But if your Web app will be complex and/or on mobile you need to support phones then really you need to build two separate projects.  Of course, you could re-use the DataWindows.  They key point is you need totally different UI for phone vs. desktop, and also usually our customers only deploy a subset of features of their larger app to phone.
3. In general, we don't recommend using PFC on mobile devices for performance reasons.  For the web that is no problem since computers have so much horsepower and memory.  If you do decide to use PFC on mobile device, I would recommend to not use it heavily.

Our mobile UI design & development guide is a rather long document and a lot of this may be common sense, but anyway might be useful to take a look at it.

Hope this helps!