Trying to use the Finder to open multiple instances of an application on Mac OS X will simply cause the first instance to come to the foreground. To get around this, use the open command from the command line with the -n option. The -n option opens a new instance of the application even if one is already running.
For example, if the Data Center software is located on the user's Desktop, using the following command in the Terminal will open a new instance of the Data Center software.
open -n "/Users/user/Desktop/Data Center.app"
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比如我想开启两个floating clock，可以这么写
open -n '/Applications/SimpleFloatingClock.app/'