How do I open multiple instances of an app?
Because OSX is just unix, you can use a terminal to run the original binary that's stored in the *.app directory. A la

/Applications/TextEdit.app/Contents/MacOS/TextEdit &amp;

Keep in mind some applications use databases to store their data which may cause conflicts or loss of data.

If you don't want to use the terminal, then you can make a shortcut icon that runs this command using the built in Automater app