You are now in a time when there are alternatives to Flash; note that YouTube just stopped using Flash as its video player, switching to an HTML5 based solution: [
^].
While this astoundingly full-featured on-line color picker application has been around for years, it now makes extensive use of jQuery: [
^].
Specifically, you can use JavaScript, WebGL, HTML5, CSS, etc., to create powerful web applications that will run on any browser in almost any device, such as this one: [
^].
The difficulty, I think, for someone deciding on creating an Application using this bundle of technology (what I call the "Web Stack") is that there are so many options available, so many different available frameworks for "rich," or "thin" clients, for server-side.
You will probably want to check out at a minimum:
1. jQuery
2. AngularJS
3. Node.js
Of course, there are myriad tools from Microsoft, and you can use Node.js within Visual Studio via a plug-in, use Angular via a special template, as well as jQuery. You can use MS's TypeScript to write strongly-typed code that is translated into JavaScript, or tools like AtScript from Google.
imho we are in time of great ferment, and explosive creativity, as we stumble towards whatever/whereever the future will be. JavaScript (EcmaScript) is heading towards version 6 which will make it much more like C#, imho; take a look at its features: [
^].