That first one is proprietary. The other two (PeaZip and 7-Zip) are mostly libre, but come with some proprietary components.

As to why 7-Zip is only available on non-Windows systems as a command-line tool... I'm not sure, but I assume it's that something about the way the GUI is programmed makes it only work on Windows. p7zip is the command-line backend of 7-Zip.

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