BOA Constrictor Archiver
From Just Solve the File Format Problem
BOA Constrictor Archiver, or BOA for short, is a compressed archive utility for DOS. It was developed by Ian Sutton.
It's unclear if there were any public releases other than v0.58. No earlier versions are mentioned in the documentation. If there were any later versions, they are presumably lost.
Version 0.58's native file format uses the .B58 file extension, and was expected to be incompatible with future versions of the software. The hypothetical stable format would have used extension .BOA.
Files start with ASCII "
BOA", followed by two bytes for a version number:
0x00 0x3a (0.58) for the only known version.