The parallel on the widget front is an "interaction loop", these are the hooks built in widgets that encourage interaction - by responding to content or sharing with others. The main difference between 'interaction' and 'viral' loops- not all interactions are viral, some interactions simply benefit the user through personalization or community interaction. Widgets differ slightly from social applications in that the end goal isn't always to get the user to send to a friend, widgets are typically used to provide a service to the end user, such as presenting personalized information or content.
Using a NewsGator widget as an example, he identifies a number of "interaction loops", e.g.:
- Email link - tell a friend
- Ratings - the canonical 5-star rating
- Get This link
- Create your own widget link