1. The document discusses Skype extras, which are applications that can be built and integrated into the Skype client to enrich the Skype experience. Skype extras see high download rates, with some seeing over 300,000 downloads per week.
2. Developers can publish extras through the Skype publishing studio, which provides features like localization support, licensing options, and revenue sharing models where Skype takes a cut of sales.
3. One example discussed is the Unyte application, which allows seamless application and desktop sharing directly from Skype. It has seen rapid growth since launch and integration provides benefits for both users and developers.