By default OS X will only let you run a single instance of any app, which is OK if the app is designed with multiple windows & a single instance in mind. MonoDevelop is a different beast, and sooner or later you’re going to want to run at least 2 instances of it, here’s how:
First run the AppleScript editor, and enter the following code:
do shell script "open -n /Applications/MonoDevelop.app/"
Now save the script somewhere easily accessible, make sure to set the ‘File Format’ to ‘Application’. I chose the name ‘MonoDevelop Launcher’:
Now the only problem left is the icon, it’s most likely the AppleScript icon, rather than the MonoDevelop one:
Use ‘Get Info’ to get the info for both your new launcher, and MonoDevelop. Click on the icon for MonoDevelop and press CMD+C. Now click on the icon for your script, and press CMD+V. The icon should now be correct:
References: Based on answer by ‘Subfuzion’ as StackOverflow