iGoogle added a new feature that lets you share gadgets with your contacts and allow them to edit the content from your gadgets. For example, if you share the To-Do list gadget with your friends or co-workers, they'll receive an invitation to add the gadget to their iGoogle pages and every time someone makes a change it will be propagated to all the instances of your shared gadget.
For now, the list of collaborative gadgets includes: to-do lists, notebooks, crossword puzzles, birthday reminders, but we'll see more interesting ideas as gadget developers can easily add this new feature.
"It's now possible for multiple instances of a gadget - on the home pages of different users - to access the same user-preference data, the part of the gadget state that is hosted by iGoogle. (...) It's a simple sharing model - last write wins, and a reload is required to see changes made by others."
To share a gadget, click on the small arrow from the title bar and select "Share this gadget". For most gadgets, you can invite your contacts to use them and optionally send your settings, but collaborative gadgets have a different dialog: