Zmarties

Yahoo! and Google have both just released new API's for building widgets. The Google offering is new, and allows you to add the widgets to your personalized Google homepage, whereas the Yahoo! offering is at version 3 - but you need to have downloaded the Yahoo! Widget engine to run the widgets (hence they are limited to Windows and OSX).

Both types of widgets are written in Javascript, so it is fairly easy to adapt from one API to the other. At the moment the Yahoo! widget gallery has 1600 entries, whereas the brand new Google widget directory has just 5 staff written samples.