Open multiple Eclipse workspaces on the Mac
By far the best solution is the OSX Eclipse Launcher presented in http://torkild.resheim.no/2012/08/opening-multiple-eclipse-instances-on.html It can be downloaded in the Marketplace http://marketplace.eclipse.org/content/osx-eclipse-launcher#.UGWfRRjCaHk
I use it everyday and like it very much! To demonstrate the simplicity of usage just take a look at the following image:
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.
Open the command line (Terminal)
Navigate to your Eclipse installation folder, for instance:
cd /Applications/eclipse/cd /Developer/Eclipse/Eclipse.app/Contents/MacOS/eclipsecd /Applications/eclipse/Eclipse.app/Contents/MacOS/eclipsecd /Users/<usernamehere>/eclipse/jee-neon/Eclipse.app/Contents/MacOS
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