A lot, actually. You can use Javascript combined with DOM to make interactive documents. All those dropdown/roll-down menus are Javascript manipulating Document Objects. There are GRAPHICS games that's made in Javascript. Not that many, but a few. I think someone actually made a Wolfenstein 3D clone in Javascript.
(Not that many levels, but it's real 3D in a browser!)The language is also a decent starting point to other stuff, like true Java and JSP