On http://stackapps.com several [Mac OS X](https://stackapps.com/questions/tagged/app+mac-os-x) applications are listed. StackApps is the StackExchange API and application and scripts site.

Personally, I use [Newt](https://stackapps.com/questions/1993/newt-question-answer-and-comment-and-rep-change-notifications-for-mac-os-x), which can display new questions, comment notifications and reputation changes from across all the StackExchange sites, including AskDifferent.

To answer some points raised [elsewhere](https://meta.stackoverflow.com/questions/142637/how-does-the-sostatus-app-work-osx):

* The SOStatus app most likely uses the [StackExchange API](http://api.stackexchange.com).
* I don't think it is Open Source; the developer does not list it on it's [Open Source software page](http://www.eosgarden.com/en/opensource/) nor is there any trace of it on their [GitHub account](https://github.com/macmade/).