Nullsoft Scriptable Install System (NSIS)

If you haven't had enough options for installation systems already, then check this one out. Developed to support Winamp this is an excellent, tiny installer (adds only 20-40k overhead to the compressed data) and supports everything you'd want to do, not to mention providing a, cough, "lovely coding experience with elements of PHP and assembly". Very widely used (visit the users page and follow some links - some very interesting applications and coding tools to be found).

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