The WRLD Windows SDK allows developers to run the WRLD API through this C# SDK on Windows devices and applications. The main SDK method is embedding a 3D map. WRLD is a company that creates and provides interactive 3D maps for a variety of operating systems/devices, such as iOS, Android, OSX, OculusVR, and WebGL.
MMOG designer ArenaNet is transforming its popular Guild Wars 2 by opening up its code to be redeployed by users via APIs. Players can make their own iOS and Android apps as well as build tools to use in the game. The Guild Wars 2 API will likely become extremely popular among its huge user base for what Time Magazine called "#1 VideoGame of 2012."
When it comes to map mashups there's no doubt that Google Maps leads the way. On ProgrammableWeb we list 1,964 Google Maps mashups, almost four times as many as any other API. This popularity makes utilities built on top of Google Maps especially interesting, such as this contextual menu control, which pops up a menu when the user right clicks.