From br41n software:
SABnzbd is a free news client with many abilities, such as dDownload files from your newshost. Access the news client from any internet connection. Connect from work, school, wherever and tell SABnzbd to download. Your downloads are ready when you get home. No more repairing or unpacking. SABnzbd handles the dirty work for you. You tell it what to download and when it is done, SABnzbd will repair the download, unpack it, and clean up the mess. Leaving you with nothing but the files you wanted. Full nzb support. This is the OS X build - everything packed in one convenient universal application.