> but applets are not supported any more by windows,
You just need the Java runtime environment (JRE) to run applets on you machine.
Java still has a use, but not any more on 'popular websites'; Java is used often for graphical simulations of physics, maths, network principals - it can still be found, and it certainly works on windows, the only change is that MS don't package a proprietry JVM with Windows anymore; which is honestly a good thing for Java.
It seems strange that Applets aren't so popular, as Java is a popular programming language. But i've never used flash so i couldn't really compare why you would choose one over the other.