for macs use stuffit expander. http://my.smithmicro.com/mac/stuffit/expander.html
sign up for the FREE stuffit expander
, not to be confused with free trial or free deluxe demo. Trust me, it's not a scam, you just have to sign up and they will send you an email with the link.
This one is the best for macs (and pc's) because all you do is double click on rar, and it automatically extracts it into a new folder in the same directory for you!
now if anyone knows how to create rars on a mac, please let me know!