Nicecast is a very nice audio streaming tool for the Mac. This app has been made with a lot of attention to detail, and you can tell by simply launching it for the first time. It was designed to allow you to stream music from your Mac to any computer or device with an Internet connection. You don't need any additional software on other computers to listen to broadcasts created using Nicecast. As a matter of fact, Nicecast creates a web server on your Mac and it places an M3U file on that server. Any device that can play an M3U file will be able to connect to your broadcasts.
Nicecast can "hijack" the audio of pretty much any application that you have on your Mac. The default app that is used is iTunes, and that makes sense, since it is the musical hub of your Mac. When you start a broadcast, Nicecast will relaunch iTunes in order to hijack it. You can then change your settings to set the quality of your streams, which will have an influence on the bandwidth used, and to add effects to your broadcast.
Nicecast automatically forwards ports when your router is compatible with uPNP. This allows you to broadcast to users outside your home network.