JigdoOSX provides a port of the Jigdo download tool to the Mac OS. It is currently accessible from the Terminal and also via a Mac OS X GUI (AquaJigdo).
Goron (formerly Leviathan) is a HTTP-webserver with HTTP/1.1 support. It's very flexible and extandable. It comes with an easy-to-use GUI, an Apple iTunes RemoteControll, a webadmin plugin and the ability to add PHP or Perl support.