We can add many of the default gadgets available from Yahoo! which includes some news feeds, weather, finance, Yahoo Maps and more.
In addition to these gadgets, there are some Open Apps (BETA) available for adding to our personalized page.
For developers, Yahoo has an application editor for My Yahoo!, where we can build Open apps and test it.
As of now, we cannot publish the apps for other users in the world (Publish button is disabled).
But we can test/use the app ourselves, invite friends to add/use in their My Yahoo! page.