Basically MSOEngine (Matt's Stack Overflow Engine) is an Objective-C library that communicates with Stack Overflow.
It uses the MIT License.
You can find (the new and improved version) here.
This currently runs on both Mac OS X and iPhone. The new version has been pushed up to GitHub. It works the same was as before, and you don't have to do a thing to make it work with the iPhone OS.
See README in the GitHub link and it explains how to use it. It's a little complex, and requires at least a level 5 in reading documentation.
You can contact me at matt (at) mattsapps (dot) com