This directory is the installation directory of the app for the application area.
Every app developer can install their apps in their own directory.
If you're looking for code or information about apps you've installed, this is it.
The app should never be adapted or changed directly, otherwise the changes will be lost during an update.
Use the APPNET OS Evil Extend option to adapt the apps and replace the templates via APPNET OS Custom Override in the custom directory.
Further information on the topics can be found in the tutorials.