I built a Rails App that could be used by environmental groups to monitor water quality. It uses the Google Maps API. Users can create locations by entering GPS coordinates, or by clicking on a map. Clicking a location on the map automatically enters the GPS coordinates into the form. It also has different custom map icons depending on the type of location.
This project took about 8 hours all told. It uses Devise for authentication and Bootstrap for the layout. Feel free to check out the public version on heroku. You will need to create an account in order to add locations.