http://nsis.sourceforge.net/Main_Page
From NSIS Wiki
NSIS (Nullsoft Scriptable Install System) is a
professional open source system to create Windows
installers. It is designed to be as small and
flexible as possible and is therefore very
suitable for internet distribution.
Being a user's first experience with your
product, a stable and reliable installer is an
important component of succesful software. With
NSIS you can create such installers that are
capable of doing everything that is needed to
setup your software.
NSIS is script-based and allows you to create the
logic to handle even the most complex installation
tasks. Many plug-ins and scripts are already
available: you can create web installers,
communicate with Windows and other software
components, install or update shared components
and more.