The Unarchiver is great. It is promoted as "a much more capable replacement for 'Archive Utility.app', the built-in archive unpacker program on Mac OS X"
I hate RAR with a passion but sometimes you've got to open one. I too like The Unarchiver. It handles all sorts of things, so you don't need a separate RAR opener, another one for 7zip, it can open my legacy Amiga LHA files, etc.
The Unarchiver is great. It is promoted as "a much more capable replacement for 'Archive Utility.app', the built-in archive unpacker program on Mac OS X"