Xnews hasn’t been updated since May 2009 and looks to have been abandoned. Xnews does not appear to have been tested on operating systems newer than Windows XP, and there is no Mac version. Xnews also does not support NZB downloading, which is now the primary way that people access Usenet.
If you want a good NZB downloader, take a look at our SuperNZB program. It runs on Windows and Mac.