Nudist CompassAlso available as Android App.
I use this app a lot when travelling. It shows all naturist places on a map with reviews from visitors. Unfortunately there is not enough moderation on the app, so not all information is reliable. But you can be sure if a certain place has many reviews, it is genuine.
You can also add new naturist locations.
If we all start using this app more frequently, the information will become better and better!
Website in German and English. It has a list of more than 3000 naturist locations.
Very useful is the .kmz file you can download, so you can add all these points of interest to any map you are already using (Like apps using OpenStreetMap)