A proxy server is responsible for transferring data between two web sites.
One of the main problems with eMule, that's why it's not available to those mac operating systems which are not compatible with the protocol, is its lack of a proxy server. Other cool Mac alternatives to eMule would be MySpace, Giganews, Facebook, Foursquare, Twitter, Technorati, Urchin, FourSquare, Tagged, YouTube and Vimeo. Other interesting Mac alternative to eMule would be Bit torrent (FSF), also referred as BTF. EMule isn't available for Mac yet but there are other alternatives which runs on newer Mac operating systems with similar functionality.
