[joecool1029]

For compressing, but for uncompressing you can literally build unrar from source if you want, here's the source: https://www.rarlab.com/rar/unrarsrc-7.1.1.tar.gz

I do want to point out that for transmitting compresed files 7z is fine, but as a longer term backup format rar has a lot of functionality that makes it convenient (built in verification, parity generation/repair, support for all the extended filesystem attributes)

[o11c]

That's not open source, only public source, which is a major limitation.

[joecool1029]

It's open source. Here's the license: https://github.com/pmachapman/unrar/blob/master/license.txt

(There is one single restriction added that you are not allowed to create a rar archiver with it, only a tool to handle existing rar files)

[o11c]

Other than that, Mrs. Lincoln, how was the play?

A single restriction is enough to ruin everything.