Open Unity project in multiple editors

Although not exactly opening the same project, the end result is the same:

Simply create symbolic links to an existing project and open them in the editor.

Original project path: D:/projects/MyUnityProject

Open command line prompt in Administration mode:

D:
CD projects
mkdir MyUnityProjectClone
cd MyUNityProjectClone
mklink /d Assets D:\projects\MyUnityProject\Assets
mklink /d ProjectSettings D:\projects\MyUnityProject\ProjectSettings

Source: http://www.gamasutra.com/blogs/AshkanSaeediMazdeh/20130716/196367/Openning_a_Unity_project_in_multiple_editors_for_goodness_of_multiplayer_game_development.php