My latest tinker project is a Twitterific like application that monitors your Github dashboard, showing both updates to who you follow and updates on any repositories, yours or forks of yours. From what I've seen Github's API supports all of this.
To accomplish this I'm extending Steven Degutis's CocoaREST framework to support the Github API in my fork of the project. So far I've got repository listings by username, and showing forks in the network setup. There's a lot more to integrate but I'm not sure how much I want to demo in the UI.
I also added a tab strictly for Github, with the idea being a tab for each API supported, but I haven't dug into any other API beyond Twitter or Github's I'm not sure when those will come. Patches welcome of course.