Nicecast can be used to create a stream of your own music (to which you own the copyright), of other copyright-free music, of your own talk or call-in show, as a baby monitor, and many other ways. All of these are perfectly legal and have no fees associated with them.
You can also use Nicecast to stream copyrighted audio. Note that this use case may have regulations and minor fees associated with it. Please see this link for more details on US webcasting laws.
Laws in your other countries may vary, so be sure to consult a lawyer if you're planning a commercial station.