Being based on Firefox, Nvu is available for various OSes like MS Windows, MacOS, Linux (different flavours like Fedora, Debian, Linspire, etc.). I just found out from the changelog of SkyOS that they have ported Nvu to SkyOS!. This just proves that Nvu (and hence mozilla based applications) is truly portable to different operating systems.
Check out their screen shots on their main page where you can see open source applications like Gimp, Firefox, Thunderbird, Nvu, etc. in action. A closed source operating system other than MS Windows running open source applications....Intersting!