There's a shareware rar program for Linux, which must be registered within 40 days of use if you are going to keep using it. This is written by Martin Meredith. It is in the Ubuntu multiverse repository. You didn't say what distro you're using, so I can't give you distro-specific info.
There's also an unrar implementation by Ying-Chun Liu, which is in the universe repository. The homepage is here