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.
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
Action Script 3 coding sample
based on a start & stop button (instance names button_1 & button_2)
Dr Tim Kitchen's Journal - Creativity in Education 