ClickOnce Deployment Manifest
Files that have the .application file extension are ClickOnce Deployment Manifest files. These are from Microsoft and are used to deploy programs, these files are xml files that contain the information regarding the actual application to be deployed.
ClickOnce is a part of the Microsoft.NET framework and is similar to Java Web Start. The files are opened either by using a double click or run in the context menu, then the manifest is checked and the program is either downloaded and installed, ran in Web Browser or installed or run from CD or DVD etc.