File Extension EXO File Format System file EXO stands for System file. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question What app will play EXO files? Data storage information What are the differences between Network File System (NFS) and Network Information System (NIS)?