I would recommend you a simple three-fold approach:<p>1. Think of an existing Web application that you like a lot<p>2. Think of a feature it's either missing or something that can be simplified in the app<p>3. Build a stripped-down version of the app in your spare time as a side project. Launch, gather feedback &#38; analytics, improve, repeat.<p>This approach will solve your concern with finding the idea and executing it with limited resources.