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.
The 7-Zip derivative intended for the modern Windows experience
NanaZip is an open source file archiver intended for the modern Windows experience, forked from the sourcecode of well-known open source file archiver 7-Zip. Sourcecode is hosted at https://github.com/M2Team/NanaZip.