An APP file is an application that is executed in the Mac Operating System and is similar to the common EXE extension used in the Windows Operating Systems.
These files are strictly designed to run in the Mac Operating System but can be viewed as a folder in Linux and Unix based Operating Systems.
.app File Extension
Developer:
Apple
什么是 app 档案以及打开它的方法 - Mac OS X Application File
开发商:
Apple