Archiver 3.03, often abbreviated as Arc303, is the TI’s equivalent of ZIP files they are compressed files that usually contain more than one other files inside them.
Usually these end with an ‘@’ character to indicate they are archived, although some PC distributions may use a .ARC or .ARK extension instead. To extract the files, you will need a copy of Archiver 3.03 found at http://ftp.whtech.com