One guy just posted a new topic in the French forum about the Dutch/Belgian - Prussian/German condominium of the Neutral Moresnet.
It's said on Wikipedia (in different languages) its official currency remained the French franc, as no decision made after Napoleon's "imprisonment" in Saint-Helena. However, there was a common use of currencies from both countries (Dutch Guilder replaced by Belgian franc, later part of LMU ; different types of thaler currencies, followed by the Reichsmark), and, as the main reason of such creation, 3 different objects which look like local coins, as mentioned here.
Any opinion about this numismatic ufo?