Windows XP!! 1 Month before the deadline and in terms of market share Microsoft's fastest-growing operating system is the never-say-die operating system Windows XP. It is still used on just under one third of all desktops, second only to windows 7.
Which goes to prove that old software do not die. They just become more and more popular as they age. Now after Microsoft stops supporting Windows XP, I can expect to see all kinds of services popping up offering third part support for Windows XP.