The official PlayFab C# SDK by PlayFab calls the PlayFab REST API to access game backend services. Features include analytics, player accounts, and virtual goods. TLS v1.1 is needed to connect to the Playfab service.
There's no doubt that Wikipedia is a giant store of information. And yes, they have an API, but the data isn't exactly structured. But that didn't stop Jim Blackler, who created Quizipedia, a fun game based off of Wikipedia entries.
Following-up on yesterday's post on the best new mashups, here is another notable mashup from this past week, yesterday's Mashup of the Day: Gaiagi Driver. What is it? It's a mashed-up 3D driving simulator that uses a lot of web APIs across multiple windows to create a unique driving experience. Give it a starting and ending address and it follows the path created by the directions and shows your present position in four different views: