Notgeld is German for “emergency money” or “necessity money”. They are forms of currency issued by an institution not authorized for money emission, usually when the central bank cannot print money. Although it is not legal tender, it is used as mutually accepted means of payment in particular towns or areas. The most notable use of notgeld occurred in Germany and Austria-Hungary around the end of the first World War.
Here’s a collection of various notgeld designs. Some are quite colorfully decorated and have unique typography.