Part of the reason it's historically sold so well is that its particular combination of features is difficult to get economically in other ways. If you want, sa

Part of the reason it's historically sold so well is that its particular combination of features is difficult to get economically in other ways. If you want, say, a blinking LED without a microcontroller, it can't really be done without a 555 except at severe penalty in cost, complexity, or both. Any analog solution involving an op-amp, for example, has to deal with the fact that an op-amp is usually more expensive than a 555! (Example: TI's cheapest 555 is the NE555 in TSSOP-8 package at $0.05, and their cheapest op-amp is the LM321LV in SOT23-5 package at $0.04, actually slightly cheaper than I remember last time I went looking for the cheapest op-amp money could buy. But the op-amp will require more supporting components, increasing total cost.) That's not true for voltage regulators: there are many other parts that do what a 7805 does and many ways to build that function, some of which can sometimes end up cheaper. Of course, the previous caveat of "without a microcontroller" is quickly becoming a concern of the past, and, accordingly, the 555 isn't designed in nearly as often as it was even in 2003.