The Twitter Kit for iOS, supported by Twitter as part of the Fabric developer suite, helps developers create iOS applications that integrate various Twitter functionalities. The SDK can be used to implement easy Twitter login, composing tweets, displaying tweets, and authentication all from a 3rd party application. The iOS Twitter Kit includes "Login" for standard login, "Twitter API," for iOS driven API requests, "Tweet Views," for displaying a user's Twitter stream, "Tweet Compose," for composing and posting new tweets, and "Digits," a new way that users can verify with Twitter via their mobile phone number over SMS-based authentication.
n0tice is a simple location based public notice board system. It's completely open and unfiltered, and allows users to post any sort of notice they want, tagged with their location, and lets them read notices near them, sorted by distance. Quite a simple little idea, and if it gets a user base, it could end up being quite useful. Although first designed for iPhone, the n0tice API was quickly released to allow integration into other programs, including desktop apps.