Looking to build my skills

I have hit a brick wall. I keep making small web-apps, play around with them for a few weeks, and then throw them away into a miscellaneous folder (been growing it since 11th grade now) that is looked at from time to time to see how much I have improved.

The issue is that I have always been making things for myself, based on ideas I came up with. I want to make something that is outside of my comfort zone, from scratch.

So my request from the community: Suggest an idea for a web app that doesn't exist, the more novel or strange, the better. I will try my best to make a fully functioning prototype, not spending more than 48 hours per app.