Don't Use RAR
The rar license prohibits writing a compatible compressor?  What kind of nonsense is that?  I clicked the license link and there is a scary looking anti-reverse-engineering clause, but 1) that sounds legally dubious given how the program is distributed; and 2) there is a FOSS decompressor, and studying that may be sufficient to write a compressor without examining the non-free official compressor.The article is right that there's not much good reason to use rar these days.  It is still popular in some communities though.  So I've had occasion to run the decompressor, though not the compressor as far as I can remember.