Note: I have not tried any of these tools in depth.
However, if you're just looking to create an online video there are lots of tools including Moovly, GoAnimate, and Wideo, but there are many more similar ones.
If you're looking for what technologies you can use for web animations, you should check out the question on here called What's the best way to animate an illustration for the web?
For anything more than a simple video type animation, especially something involving much user interaction, I recommend hiring a developer/animator (like me!) to create it it for you or to learn how to do it yourself.