Internet Explorer 3, 1996
Escaping the developmental womb in the same year and month as Navigator 3, Internet Explorer 3 was Microsoft's first serious salvo in what are now known as the "browser wars." So serious, in fact, that Netscape would never, ever recover.
That Navigator had been the superior product to that point in time was indisputable. Microsoft seemingly needed a little time to fully discover the Internet, and Explorer versions 1 and 2 were less than spectacular. Nevertheless, its tight integration with Windows had gained Microsoft a solid user base. When the third iteration appeared—again at no cost and sporting cool new features such as support for multimedia, Java applets, ActiveX controls, and add-ons like Internet Mail—the worm had turned.