After I joined some Startup Weekends events in Rio, I was invited to redesign the entire app called Bubble.
Bubble was an app like Twitter, like Yelp, like FourSquare but not even close like them. I explain... Bubble was created to report any issue you might see or have in any place, anywhere. If you drive by a road and its full of hole, you could report to Bubble and everyone (who had the app installed) could see and avoid that road. If you spot a car parked in a wrong or forbiden place, your could report and so on.
Unfortunately the app is no longer available. But was a great idea.