You can clone an unlimited number of apps within your account. When you clone an app, it will clone as a Demo App.
A cloned app will duplicate your cover and the content within your Yapp in a second app with a separate URL. The new app will be published once cloned, but no one can see it until you share the URL with them.
All content can then be edited independent of the original app. If your original Yapp had a News Feed, Social Feed, or Crowd Pics page full of user posts, those posts won't transfer, so you'll have a fresh page.
To clone an app:
Go to your dashboard at http://yapp.us/apps, find the app you want to clone, and click the gear icon in the upper right corner.
Your app will then clone and will be called "[Name of First App] copy". Here's how to rename an app.