This is a tool that lets you use MacBook Pro Retina's highest and unsupported resolutions. As an example, a Retina MacBook Pro 13" can be set to 3360×2100 maximum resolution, as opposed to Apple's max supported 1680×1050. It is accessible from the menu bar.
You should prefer resolutions marked with
For more practical results, add RDM.app to your Login Items in System Preferences
This software was studied and released here and here by its original authors. I just improved the build system and Makefile, fixed the icon, added support for easy installable package (PKG, DMG) and improved the way menu is displayed. I don't know what is the license by its authors because it came 100% uncommented and undocumented. But I'm sure they would enjoy you to freely use it. Me too.
Want installable binary package? It is here.