What is a DNN App?
DNN Apps are a like modules on steroids. They are easy to modify and template, and install per portal (not globally on the entire system). To make this possible, you must first install the 2sxc App engine, instructions here.
Use it as is, or create your own templates/output.
You can also use this to discover how to create drag-and-drop uploads in your Apps.
What is also neat is the ability to actually just show images, and later on extend them with additional meta-data. A must-discover for new app-developers.
Discover it in this 100-Second-Video (this is for the old V1, V2 is way better :) )