I am developing an application in using Ruby on Rails, mostly as an excuse to learn the language.
This is not intended to be a web-based application - and perhaps I
You do not specifically say whether it is supposed to be a GUI application or not. From the other answers, I would guess so.
Therefore, you need to clarify what your goals are. RoR is a specialized framework for web applications. If your goal is to learn RoR, I'd say to get yourself some inexpensive web hosting and make yourself an app. If your goal is to learn Ruby, not necessarily Rails, then Shoes, IronRuby, JRuby, MacRuby and others may be good options to look at.