This app makes it very simple to look up coordinates using the Dutch RD grid or Rijksdriehoek system. No hassle with romers and large paper maps, but direct results.
You can lookup coordinates on the map, and you can also enter them manually. It is also possible to find your current location.
The coordinate system is called Rijksdriehoek, and is maintained by the Dutch Cadastre. These coordinates are used on their maps, and Dutch scouting groups use these maps very extensively.
This app uses the Proj4j library from OSGeo: