I still don't quite grok GWT, even having known about it for something like a decade. Is it a web application frontend thing that compiles Java to JavaScript?
Basically yes, you write in Java and it compiles it full-client side JavaScript application. But it also has a lot of goodies, like "templating" or rather binding DOM to code, internationalization, code splitting (so not everything is loaded upfront), client-server communication and other things needed in front development. You typically develop one-page applications with it (fully client side).