An interesting thing about JavaScript is that it always runs inside a host environment. The browser is the most popular host environment, but it is not the only one. JavaScript can run on the server, on the desktop, and in rich media. Today, you can use JavaScript to do all of this:
Create rich and powerful web applications (the kind of applications that run inside the web browser, such as Gmail)
Write server-side code such as ASP scripts or, for example, code that is run using Rhino (a JavaScript engine written in Java)
Create rich media applications (Flash, Flex) using ActionScript, which is based on ECMAScript
Write scripts that automate administrative tasks on your Windows desktop, using Windows Scripting Host
Write extensions/plugins for a plethora of desktop application such as Firefox, Dreamweaver, and Fiddler
Create web applications that store information in an off-line database on the user's desktop, using Google Gears
Create Yahoo! Widgets, Mac Dashboard widgets, or Adobe Air applications that run on your desktop
This is by no means an extensive list. JavaScript started inside web pages, but today it's safe to say it is practically everywhere.