An AS3PROJ file is a project file created by FlashDevelop, a free open source programming IDE for developing Flash and Web applications. It saves all the project related information and settings applied by the user using the FlashDevelop IDE. Information stored in an AS3PROJ file includes build settings, references to project source files, and options for generating the output .swf file. When a new project is created, it is saved as AS3PROJ file at the same location that is specified by user for saving the project related data.
AS3PROJ File Format
An AS3PROJ file is saved in XML file format that is a universal file format for exchange of information. It can be opened in any text editor such as Notepad, Notepad++ and Atom to examine the contents.