This is an add-on to ACF that adds a field to select multiple Google Map points in a post.
The plugin is a modified extended version of the Advanced Custom Fields: Coordinates made by Stupid Studio and is found here: http://wordpress.org/plugins/advanced-custom-fields-coordinates/
This software is licensed under the GNU General Public License version 3. See gpl.txt included with this software for more detail.
The plugin relies on the Google Maps API. It does not use an API-key and is therefore operating under the restrictions of the free Google Maps API, which should be plenty for most backend usage.