NSIS, which stands for "Nullsoft Scriptable Installation System", is a free scriptable win32 installer/uninstaller system that doesn't suck and isn't huge. It was originally created by Nullsoft to distribute Winamp and its plug-ins, but is now a system used to distribute hundreds of applications.
NSIS creates installers that are capable of installing, uninstalling, setting system settings, extracting files, etc. Pretty much anything. Because it's based on script files, you can fully control every part of your installers. The script language support variables, functions, string manipulation, just like a normal programming language - but designed for the creation of installers.
Even with all these features, NSIS is still the smallest installer system available. With the default options, it has an overhead of only 34 KB. NSIS installers don't bother decompressing themselves three different times, telling the user to "please wait". They get to the point and get the job done.
NSIS is released under an open source license (it is actually the zlib/libpng license, which is approved by opensource.org). What does this mean? It means that if you want to add the functionality you need to NSIS, you can. It means if you want to make your own custom version of NSIS (or some product that includes NSIS), and sell it, you can. Or if you just want to distribute your software using NSIS, you sure as hell can. NSIS 2 is now being developed by a team of open source developers.
The result of all of this is an installation system that lets you compile nice little scripts into tiny installers. Many features are supported, and the whole thing just works pretty damn well (at least, we think).
\b Approximately 20-40k overhead over compressed data size (depending on features enabled, compression algorithm, and so on - the default options are ~34k).
\b Easy to use plug-in system (lots of plug-ins for creation of custom dialogs, internet connections, HTTP downloading, file patching, Win32 API calls etc. are included)
