Sometimes you have a project that you’re using as reference, maybe you added some functionality in a previous project or you downloaded a sample project and you are trying to recreate that thing in your new project. It would be great if you could have them both open side by side so you can compare them right?
Unfortunately if you try to open Unity by clicking the icon, it will just bring your current instance into focus, so what can be done?
Here’s a simple trick that allows you to have two instances of Unity open at once, open the second instance from the command line and point it to a project.
$ /Applications/Unity/Unity.app/Contents/MacOS/Unity -projectPath ~/projects/coolgame
Note: You cannot open the same project twice, so if you have to do that create a temporary copy of the project.