IzPack is a powerful software installers generator for the Java[tm] platform. It uses a very modular architecture that lets you make the installers work as you want, not as the software wants it to work. It is also possible to extend it to suit your needs since it has been designed with this purpose in mind from the start.
The installers generated by IzPack are independant of the target operating system. It has been running successfully on Linux/i386, FreeBSD, Solaris, MacOS X and Win32. All it needs is a Java[tm] Runtime Environment. Unfortunately, there is no Java[tm] Runtime Environment that is available under an OSI-approved license. The recent news from the Java[tm] community suggest that it will never be the case. This is a shame as it restricts both your freedom and the number of supported platforms.
IzPack is published under the GNU GPL which is a Free Software license as defined by both the Free Software Foundation and the Open Source Initiative. This means that you can freely redistribute and modify IzPack as long as you respect the GNU GPL terms.