Java applets were all over the place for many years. I remember there were tons of maths, CS and physics sites that used Java to render things like simulations

Java applets were all over the place for many years. I remember there were tons of maths, CS and physics sites that used Java to render things like simulations and algorithms. Sometimes the Java stuff was hidden: Before XMLHttpRequest I personally used Java in several web apps as a way to do messaging with the server, because Java permitted you to do arbitrary socket connections. You inserted a 0x0 applet into the page and then used the JS bridge that both IE and Netscape provided. Aside from the JVM startup time (which could be several seconds) it was pretty great, actually. I wrote a commercial audio conferencing system that showed the talk status of each participant, for example. Basically, Java applets were (were, mind you) highly successful before the advent of Flash and AJAX.