The utility you're looking for is called Activity Monitor. It's in the Applications -> Utilities folder.
When iCamSource is running on a Mac, there is a small icon in the Menubar (top of screen). You can access the iCamSource window from that icon's pop-up menu.
Many users have had success viewing multiple cameras on the same computer by running multiple instances of iCamSource.
To do that on a Mac, you'll need to make a copy of the iCamSource application for each camera. First, run the first iCamSource and set up the first camera. Then run the second copy of iCamSource and set up the second camera.
In order to watch all of the cameras on your iPhone at the same time, make sure that all instances of iCamSource have the exact same login and password entered.