Iamklaus shows how to easily launch multiple Blenders on OSX.
Coming from LInux or Windows, it is hard to understand why it is not possible having multiple Blender instances running, in order to work on different .blend files. There are different work arounds you can use. This is the one, which did work for me the best. So far I didn't have any problems.
In my short tutorial, I describe how to use a shell command and the Automator in order to have have the similar behavior like on Linux or Windows.