Abobe Flash is the 2D animation authoring software that is commonly taught in the VET/VCE IDM Course. It is very common tool for adding animation to websites.

Animator v Animation

Here is an example of what one of my students created with Flash as part of his 2011 IDM assessment …

A professional flash sample based on Coldplay’s Fix You

Other example by Jammy Dodger

Lynda.com – Flash tutorials

Adobe TV – Flash channel

Action Script 3 coding sample

based on a start & stop button (instance names button_1 & button_2)