Launchd plist file for OS X
In order to use this config file, you will need to have your stunnel.conf file set up in the default location - or you will have to edit the stunnel.plist file so that it points at your alternate location.
In addition, you will want to have the following line in your stunnel.conf file:
foreground = yes
That way, stunnel will not fork and launchd will make sure it keeps running. This plist file will make sure that stunnel keeps running as long as there is any active network interface.
I install this file in /Library/LaunchDaemons