Because .rar is a proprietary format, your standard Windows or Mac file explorer may not be able to open it natively. You will need a third-party tool like , 7-Zip , or The Unarchiver . Steps to Extract:
Use a trusted tool like WinRAR or 7-Zip.
This is the most common origin. Older forum posts from Unknown Worlds refer to "ns.rar" as a distribution package for Linux server installs or specific beta patches.