Quick Launch Introduction Compiler Documentation Update Websites | Introduction An installer is the first experience of a user with your application. Slow or unsuccesful software installations are the most irritating computer problems. A quick and user friendly installer is therefore an essential part of your software product. NSIS is a tool that allows programmers to create such installers. It is released under an open source license and is completely free for any use. NSIS installers are based on NSIS Scripts (.nsi) which can be compiled with the makensis compiler. They can also be extended with plug-ins written in C, C++, Delphi or another language.