NSIS (Nullsoft Scriptable Install System) is a tool that allows programmers to create such installers for Windows. It is released under an open source license and is completely free for any use.

NSIS, which stands for Nullsoft Scriptable Install System, is an open source scriptable installer/uninstaller system created for Windows PCs by Nullsoft, Inc..

Of course, we're very excited to see what other open source installation vendors, such as NSIS and Inno Setup, will be doing with our open source APPX library as well.