Think is a free Mind mapping Web App powered by HTML5[HTML_REMOVED]s canvas tag, Django and Google App Engine.
You can try Think out by opening its Tutorial. This will give you a feel to what Think is about. Within the tutorial you can create, delete, edit and move nodes. If you want to create your own mind maps, you must register an account which will give you the ability to create and save as many mind maps as you wish.
Think is still in its infancy as it is only version 0.2.2, but you can expect many more features to be released in the near future.