If you mean RAR files, then unrar is (apparently) in extras-testing. If you don't find it there, then look in extras-devel. It won't show up in App Manager though, so you'll need to install it from the command-line (via apt-get).

Please do read and pay attention to the warnings about the repositories. The unrar app itself should be safe, but make sure you disable the repositories after installing it, unless you're prepared to deal with the potential consequences.