This seems to be the supported native method in OS X:

cd /Applications/eclipse/

open -n Eclipse.app

Be sure to specify the ".app" version (directory); in OS X Mountain Lion erroneously using the symbolic link such as open -n eclipse, might get one GateKeeper stopping access:

"eclipse" can't be opened because it is from an unidentified developer.

Your security preferences allow installation of only apps from the Mac App Store and identified developers.

Even removing the extended attribute com.apple.quarantine does not fix that. Instead, simply using the ".app" version will rely on your previous consent, or prompt you once:

"Eclipse" is an application downloaded from the Internet. Are you sure you want to open it?

EDIT: Milhous's answer seems to be the officially supported way to do this as of 10.5. Earlier version of OS X and even 10.5 and up should still work using the following instructions though.

1. Open the command line (Terminal)

2. Navigate to your Eclipse installation folder, for instance:

   • cd /Applications/eclipse/
   • cd /Developer/Eclipse/Eclipse.app/Contents/MacOS/eclipse
   • cd /Applications/eclipse/Eclipse.app/Contents/MacOS/eclipse
   • cd /Users/<usernamehere>/eclipse/jee-neon/Eclipse.app/Contents/MacOS

3. Launch Eclipse: ./eclipse &

This last command will launch eclipse and immediately background the process.

Rinse and repeat to open as many unique instances of Eclipse as you want.

Warning

You might have to change the Tomcat server ports in order to run your project in different/multiple Tomcat instances, see Tomcat Server Error - Port 8080 already in use

Actually a much better (GUI) solution is to copy the Eclipse.app to e.g. Eclipse2.app and you'll have two Eclipse icons in Dock as well as Eclipse2 in Spotlight. Repeat as necessary.

If the question is how to easily use Eclipse with multiple different workspaces, then you have to use a kludge because shortcuts in OS X do not provide a mechanism for passing command line arguments, for example the "--data" argument that Eclipse takes to specify the workspace. While there may be different reasons to create a duplicate copy of your Eclipse install, doing it for this purpose is, IMNSHO, lame (now you have to maintain multiple eclipse configurations, plugins, etc?).

In any case, here is a workaround. Create the following script in the (single) Eclipse directory (the directory that contains Eclipse.app), and give it a ".command" suffix (e.g. eclipse-workspace2.command) so that you can create an alias from it:

#!/bin/sh
# open, as suggested by Milhous
open -n $(dirname $0)/Eclipse.app --args -data /path/to/your/other/workspace

Now create an alias to that file on your desktop or wherever you want it. You will probably have to repeat this process for each different workspace, but at least it will use the same Eclipse installation.

2018 Update since many answers are no longer valid

OS X Heigh Sierra (10.13) with Eclipse Oxygen

Go to wherever your Eclipse is installed. Right-click -> Show Package Contents -> Contents -> MacOS -> Double-click the executable called eclipse

A terminal window will open and a new instance of eclipse will start.

Note that if you close the terminal window, the new Eclipse instance will be closed also.

To make your life easier, you can drag the executable to your dock for easy access

You can create an AppleScript file to open Eclipse with a given workspace. You can even save the AppleScript file as an Application, which is equivalent to creating an alias with arguments in Windows OS.

Open Script Editor and type the following:

do shell script "open '/path/to/your/Eclipse/installation' -n --args -data /path/to/your/workspace"

For instance:

do shell script "open '/Applications/Eclipse.app' -n --args -data /MyWorkspaces/Personal" 

Press the Run button to check it's working.

This script can be saved as such, but I prefer to save it as an Application. That way I can customize the icon by copying the *.icns icon from the original Eclipse.app bundle to the script application bundle.

To open an App folder, use the "see contents" contextual menu option. It should look like this:

Where "main.scpt" is the AppleScript file and "applet.icns" is the icon from the original Eclipse bundle.

Launch terminal and run open -n /Applications/Eclipse.app for a new instance.

Lets try downloading this in your eclipse on Mac you will be able to open multiple eclipse at a time Link

Name : macOS Eclipse Launcher

Steps :

1. Go to eclipse Market place.
2. Search for "macOS Eclipse Launcher" and install.
3. It will restart .
4. Now under file menu check for open option > there you will find other projects to open also at same time .