The ShareThis SDK allows developers to access and integrate the functionality of ShareThis with mobile applications. ShareThis is an application that lets users share links to contacts, social networks, and blogs.
Twitter Kit 3 was introduced as a standalone SDK earlier this year. Originally limited to Android and iOS, Twitter has expanded support to Unity. Whether its login authorization, in-game Tweets, or sharing, Twitter Kit for Unity might change the gaming landscape through more social capability.
Gravatar is an attempt to allow users to have one globally recognized avatar. The service, around for several years, allows a user can set an image as an avatar and have it recognized on a variety of sites. Later, users can change an avatar once and have it change on every Gravatar-enabled site that they use. Though the service is somewhat well known, what is not is its robust API for developers to integrate the Gravatar service into their own sites.