If you by 'rails' mean QT, then, no, you don't need a commercial license to edit QT and/or ship them with the application. You only need a commercial license if you add to QT or edit QT (because you can, you get the source), to support your application's special needs, and for some reason you don't want to share those QT changes with the folks you sell or give your application to. If you're perfectly fine with sharing your QT changes, and you just want to keep secret the source of your own, QT-using application, then you don't need the commercial license. This is what the LGPL is for, so you just choose that one.