DxO Labs has announced DxO Perspective for Mac OS X, which is an application designed to correct perspective and horizon problems. The application is available here in the Mac App Store and is free through November 3, 2013. Otherwise, it retails for $19.99.
You can see a quick demo of how it works in the video below.[vimeo https://vimeo.com/77985343 w=640&h=360]