Earlier quoted context omitted.
That's not open source, only public source, which is a major limitation.
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)
Other than that, Mrs. Lincoln, how was the play?
A single restriction is enough to ruin everything.