Hi Rich_Art - yeah the red button you see there in the upper-left corner is the Mac equivalent of the Windows X upper-right close button, so use that upper-left red button to close the window (and also the app).

Most Mac apps also have a "Quit" menu item on the pull-down menu at the top of the screen - that is missing in the current MoI beta which may be what is confusing them. That "Quit" menu item will be there in the next MoI beta though.

For now since there isn't a Quit menu item just use the red window close button instead though.

- Michael