Open -n /Applications/ApplicationName.app Change 'ApplicationName' to whichever application you want to open. Type it in several times, corresponding to how many duplicates you would like. In this case, I opened two instances of Safari. With the release of the latest macOS, Apple has also brought significant improvements in their security system, Which has made the keygen applications not ru.
To quit (close) a Mac app normally, choose Quit from the app's menu in the menu bar, or press Command (⌘)-Q. If the app doesn't quit, follow these steps to force the app to quit.
How to force an app to quit
Force Quit Mac App
Press these three keys together: Option, Command, and Esc (Escape). Or choose Force Quit from the Apple menu in the upper-left corner of your screen. (This is similar to pressing Control-Alt-Delete on a PC.)
Then select the app in the Force Quit window and click Force Quit.
You can even force the Finder to quit, if it stops responding: Select Finder in the Force Quit window, then click Relaunch.
Learn more
How To Close Mac Apps
How to force an app to close on your iPhone, iPad, or iPod touch.