A free file archiver for extremely high compression
...You can use 7-Zip on any computer, including a computer in a commercial organization. You don't need to register or pay for 7-Zip. And there is command line version for Linux and macOS. Most of the sourcecode is under the GNU LGPL license. The unRAR code is under a mixed license with GNU LGPL + unRAR restrictions. Check the license for details.
This is and old program written in C to read from ADSM tapes without needing the database. This code has been used on AIX machines, but may work on others. No guarantees. It does need some tweeking to get working for NT backed up tapes. This was used