Running a Imac with MacOS Sierra 10.12.6 My Imessage app was not working, so in all my wisdom I thought I would uninstall it and start over. Should have checked first to see if there is a replacement app. I checked via Google and can't find one. There has to be a way to get this back on my system. I do have the system backed up, so I could restore it. Just checking if there is another way!