IBM BookManager book
IBM BookManager is IBM's legacy online documentation system, historically used mostly on mainframes, midrange (AS/400) and OS/2, although it also saw some use in other areas including AIX. IBM no longer uses it for documenting current versions of its products, but there is an immense quantity of surviving electronic documentation from the period when IBM actively used it (from the 1990s thru 2010s), particularly documentation CD-ROMs/DVD-ROMs and images thereof.
The standard extension is BOO. No public documentation is known to be available for it. The header of BOO files commonly contains an EBCDIC copyright notice (this is true even for books for ASCII-based platforms such as OS/2). The file contents is almost certainly also in EBCDIC, but it is compressed with unknown compression algorithms (likely a relative of IBM's well-known proprietary algorithms such as TERSE, but that's speculation).
https://github.com/kev009/boo2pdf is code to convert BOO files to PDF. However, it relies on using the IBM SoftCopy Reader (for 32-bit Linux)'s JAR files and native code libraries (.so files) to actually read the file. Versions of IBM's SoftCopy Reader (previously known as IBM Library Reader and before that IBM BookManager READ) also existed for Windows, AIX (any other commercial Unix systems?), OS/2, DOS (meaning PC-DOS/MS-DOS, not mainframe DOS), MVS (later known as OS/390 then z/OS), VM/CMS (later known as z/VM), and OS/400 (later IBM i5/OS and then IBM i)–but apparently *not* mainframe DOS (DOS/360, DOS/VS, DOS/VSE, z/VSE).
"application/book" is sometimes used as a MIME type but was never officially registered
