The Gmail PHP SDK by Google currently in Beta stage includes authentication and authorization with Api Keys and OAuth 2 to start project development. Additional resources include building the client object, building the service object, calling an API, and handling the result.
Instagram has updated the Content Publishing API, a subset of the Instagram Graph API endpoints, to allow members with business accounts to schedule the publication of video content. Until recently, only direct photo publishing was available through the API.
Mashup games are always fun. Those built upon FourSquare have an extra layer of enjoyment, because they're tied to the real world. In the case of City Warfare, players use various water weaponry to soak other FourSquare users.