Mihai Sucan has written an excellent article on How to make a Voice controlled SVG game over on dev.opera.com.

From the article:
The game I have built displays several objects on screen, and the object of the game is to make all the objects have the same shape and color - you can do this by issuing voice commands ot the page, such as "change the blue squares to red triangles" or "switch the yellow shapes to circles". Once a player does so they win and the game ends. The game allows you to change various parameters such as the number of objects and players.