.APPDOWNLOAD File Extension
File TypeMac App Store Partially Downloaded App
What is an APPDOWNLOAD file?
An APPDOWNLOAD file is a file created by App Store, a program included with Mac OS X 10.6.6 or later that allows users to purchase macOS (OS X) software. It saves the contents of a purchased .APP file as it's being downloaded from the store.
When the download is complete, the ".appdownload" file extension is removed from the downloaded application in the /Applications/ directory.