Guys i’ve already searched over the web but the results never were effective,
How to open two or more Unity3D Instances over Mac OSX Lion?
If for some reason you can’t get the open project dialog to appear at startup by holding down the key on OSX (not sure what it is, but on Windows it’s Alt), you can get it to show up by changing your preferences.
Go to Edit > Preferences > General > Show Project Wizard at Startup
You should now be able to see the dialog when you start Unity, and have multiple projects open at the same time.
The option is turned on, i’ve tried to open holding the Command key, Alt key and Control key, with no result. Every time I double click the Unity App inside the Applications folder the current instance of unity turns active 
I rarely ever use Mac, so I have no idea whether this is the solution you need, but by the sounds of it OSX uses one instance of an application by default.
Perhaps try this?:
It’s very simple. Go to your Applications folder->Copy the Unity folder and paste it in the Applications folder with some other name like this
Now copy the alias to your desktop and that’s it open 2 different instances of Unity at the same instance.
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Once i taught about this but them realized it was insane, maybe because of my Windows background.
Thanks for the help!
It’s simple in windows too. You just create a shortcut on your desktop and then drag it on to your Start items.
That’s it you could now open multiple instances with the same shortcut. How’s that
Hi,
i have one simple way to open multiple instances of Unity on MAC,
go to Finder/Applications/Unity3d…
then Right click on Unity3d.app and go for ‘show package contents’,
then go to Contents/MacOS and click on ‘Unity’,
this will open unity3d new instance , using this way you will have any no of unity3d instances on MAC osx!
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Please all bear in mind that running multiple copies of Unity on a single machine is not something that is expected to work, and isn’t something that is ever tested for. It’s not a supported configuration. If it works for you then great. If not, then sorry about that.
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Its 2014, and i still can’t open 2 projects simultaneously without extra magic…
I can understand i can’t open the same project twice: temp files overlapping, registry conflicts, whatever.
But why i can’t open 2 different projects at the same time out-of-box?
Thats worked for me. Thank you…
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In terminal only write
open -na Unity
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works for me,really thank you!
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works bro, thank you, you know also to show few project in sourcetree ? im new on imac