MSOEngine
Basically MSOEngine (Matt's Stack Overflow Engine) is an Objective-C library that communicates with SO. The public version basically sucks, it has NO memory management, and is very inefficient. I am currently doing a complete rewrite of it, which I will push up to github once I finish it up and I'm satisfied with it.
I currently (stupidly) don't have a license attached to it. That's coming with the next, rewritten version.
You can find (the crappy version) here with a new version that doesn't suck coming soon (I hope).
This is currently only for OSX, but it's extremely easy to get it working with the iPhone, native iPhone support coming in the next version that doesn't suck.
I have written both of these in my spare time while I'm not studying for finals/AP exams (I'm in high school /listens to heads exploding)
Sample
MSOEngine *engine = [[MSOEngine alloc] init];
[engine setURL:url];
[engine setAPIKey:key];
NSString *users = [msoengine getUserID:167586 forKey:@"up_vote_count"];
NSArray *questions =[msoengine getQuestions:@"title"];
NSString *stats = [msoengine getStats:@"badges_per_minute"];
NOTE: this is using the public version. The new version is slightly different. It's also more complex, but it's less requests to the poor server.
Contact
You can contact me at matt (at) mattsapps (dot) com