For this listing, I am indebted to two numismatists, Mr. William R. Harmon (former president of the Esperanto League of North America, and current Chief Delegate for the American branch of the Universala Esperanto-Asocio) and Mr. Chaim Dov Shiboleth. They each imparted some invaluable knowledge to me about the 2 series of Esperanto coinage. When I separately asked them for a few meager details, they supplied me with many more seemingly unmanageable facts than what I originally bargained for. I was actually bowled over by the mini-avalanches of data, which I then attempted to consolidate into a single tsunami. Both men deserve all the credit for this little-known factual material. What follows is an immoderately condensed/adulterated version of what I received. Let us begin with the more modern Stelo series:
This rebirth of an Esperantist communal currency was the result of a very ambitious initiative of Andreas Cseh (Andreo Cxe), who in 1942 founded the “Universala Ligo” (Universal League), based in The Hague, Netherlands, at the site of the current International Esperanto-Institute (I.E.I.). This event took place in secrecy on April 14, 1942 (the 25th anniversary of the death of Ludovic Lazarus Zamenhof), during the German occupation of that country. Esperanto had been banned by the Nazis, and their constituents were persecuted; many of its speakers were exterminated. The Ligo, whose mission statement was to unite mankind in harmony through the use of a common language, gained a substantial Dutch and international following in the years after WW2, with more than 15,000 members in the early '50s. During the 1st international assembly of the League on the 16th of March 1946 in The Hague, a decision was made to re-introduce a common world currency with an internationally stable value. Theirs would be an experiment in achieving peace via international economics; in proving to the world that the global conflicts caused by international economic pressures could be resolved by the use of this revolutionary currency. The noble task would fall upon the Stelo (star, one of the symbols of the Esperanto movement), and its value was to be fixed at 1 Stelo = 1 standard loaf of bread, which at the time cost 0.25 Dutch Guilders. That same year, the Ligo started printing coupons (Premio-Kupono) with the value in Steloj, for internal use (payment of activities, leaflets, prize-money, etc...). These were widely used within the movement up until the 1980s.
The minting of the League's first coinage, dated 1959, commenced on June 28, 1960. They were proudly minted in an optimistically large amount by the Royal Dutch Mint (Rijksmunt) in Utrecht. The slogan on the 1 Stelo is “One world, one language, one money”; the 5 Steloj had “The world is one nation, mankind one people”; the 10 Steloj featured the “kreinto” (creator) of Esperanto. Exceeding expectations, the sale of the coins rapidly covered the cost of production. A 25 Steloj was minted in 1965 (I purchased mine from Mr. Frank S. Robinson). These coins actually circulated, though not under any governmental aegis. They were utilized as a unit of account for sales of books and other merchandise within the Netherlands Chapter of the League, and perhaps were even valid for purchasing items at other associated outlets anywhere in the world. These coins remained in use for quite a long time, certainly for more than 30 years, until the Ligo declined in popularity and importance. In 1974, the price of the Stelo was revalued at 0.50 Dutch Guilders and its previous connection to the price of bread was terminated. In 1977, the Stelo was fixed at a new constant, the consumer price-index, which is based on a percentage of the theoretical monthly purchases of an “average” family (the same system used nowadays to calculate minimum wages). The idea behind this was that this index would not be as heavily influenced by inflation as the European currencies were at the time. But because of theoretical differences regarding the key to calculating the value of the Stelo, fierce internal dispute arose between the members of the League's board of directors, finally leading to the departure of its Cashier and financial expert, Mr. Laurence Mee. From the 1980s onwards, the activities of the League stagnated due to lack of new members, until finally in 1993 the Ligo was disbanded and their assets, including the entire remaining stock of coins, were bequeathed to the U.E.A. in Rotterdam. The dream of a common world currency leading to international concord had sadly enough not materialized.
Now let us travel backwards in time. Decades earlier, an initial breakthrough was achieved with the Spesmilo series: René de Saussure was the visionary who first proposed a stable, gold-based international monetary system which could easily be converted into many existing currencies of the era. In May of 1907, he published his project for an international currency in a special edition of Scienca Revuo (Scientific Review). Therein, he also devised the Esperanto root word “speso”, and the requisite decimal terms, from the French “espéce” (coinage). He received many letters from peers and confreres who generally approved of the concept; among the most pleased was the originator of Esperanto himself, Dr. Zamenhof. He urged de Saussure to “not sway from it” and to do everything in his power “to obtain for it the sanction” of the 3rd International Esperanto Congress later that year in Cambridge, England. De Saussure's proposal turned out successfully, and the Spesmilo system was widely and favorably advertised and employed by the U.E.A. (World Esperanto Association), which had been founded on April 28, 1908. Though de Saussure continued to make brilliant contributions to Esperanto, he was later expelled from its Academy for attempting to launch a newer language called “Nov-Esperanto”.
As examples of this coinage, 2 denominations were minted in 1912, in very small quantities, by the Swiss firm Holy Frères: a 1 Spesmilo (“milo” meaning “thousand”; 1,000 spesoj; I purchased mine from Aspen Coins), and a 2 Spesmiloj (2,000 spesoj). The aim was to sell them at the 1913 International Esperanto Congress in Bern. It is possible, although they were not intended for general use at that phase, that they seemingly saw some limited circulation. On these medallions, the dates 1887-1912 suggest not the 50th anniversary of the International Esperanto Congress (the 1st one was in 1905), but the 25 years that had passed since Dr. Zamenhof published his Unua Libro (First Book) in 1887 under the nom de guerre “Doktoro Esperanto”. Three additional patterns may have been produced for a minting that never occurred: spesdeko (10 spesoj), spescento (100 spesoj), spesdekmilo (10,000 spesoj).
The major result of de Saussure's article was that it prompted a German by the name of Dr. Herbert F. Höveler, living in Great Britain and an avid follower of the Esperanto movement, to establish the “Cxekbanko Esperantista” in September of 1908. He embraced the idea of an utopian currency, and under the alias “E. Cxefecx” (pronounced “Chefech”), he founded this international deposit bank. Its home office was in Merton Abbey, London; it also had a branch in Dresden and one in Moscow. The new arrangement, which was an immediate success, would utilize special “checks” payable by this bank; some of them bore the same unifying slogan which later appeared on the Universala Ligo's smallest coin: “Unu Mondo-Unu Lingvo-Unu Mono”. The brotherhood often dealt in small sums for miscellaneous transactions amongst themselves in foreign countries, could now debit their accounts or make payments to the accounts of their fellowmen. During that pre-war period, the catalogs of Esperanto bookstores and magazine subscriptions had their prices shown in Spesmiloj. Membership fees in their organizations were also paid in that currency; during International Esperanto Congresses, payments small and large (even in the restaurants) were paid by those checks. By 1914, this handy and inexpensive system had 730 clients in 43 countries. After the outbreak of World War I, their activities were severely limited. With the death of Höveler in 1918 there was no successor to continue the operation, so it effectively ceased to function. All creditors were repaid. Since the timing appears to be right, we can speculate that the Spesmilo coins may have actually been commissioned by the “Cxekbanko Esperantista”; or if not, then by some enterprising Swiss Esperantist(s).
Afterwards, Dreves Uitterdijk (an old but very active pioneer in the Esperanto movement) and J. Hengel tried to revive the once-promising Spesmilo monetary system. In 1927 they founded the “Universala Spesmila Banko” (Universal Spesmila Bank), and because the Netherlands was one of the few nations whose currency stayed stable during the period, its headquarters was in Laren. They issued several Spesmiloj notes (also backed by gold, with the same idealistic slogan mentioned above) but without favorable results; they disappeared in the early 1930s.

To learn more about Esperanto, a great place to start would be ELNA: http://www.esperanto-usa.org/

The Universala Ligo (Universal League) was an Esperantist world-government organisation based in the Netherlands that promoted Esperanto as the universal language, and the Stelo (Star) as a universal currency unit. The motto Unu Mondo, Unu Lingvo, Unu Mono that appears on the 1959 1stelo coin means One World, One Language, One Currency. The Stelo had its origins in the aftermath of World War 2 when 1 Stelo coupons were issued in the Netherlands. Universalo Ligo in 1959 also produced 10 Steloj Cupronickel, Weight: 9.0 g, Diameter: 28.0 mm, Plain Edge with a mintage of 10,000 pieces. It featuring 5-pointed star as obverse and portrait of Dr L L Zamenhof on reserve.

In 1965 Universalo Ligo produced 25 Steloj coin in three different metals, having the same obverse and reserve as on 1959 10 Steloj coin. these are:

01. Cupronickel, Weight: 19.0 g, Diameter: 37.8 mm, Plain Edge with a mintage of 1,000 pieces 

02. Silver, Weight: 25.0 g, Diameter: 37.8 mm, Plain Edge with a mintage of 5,000 pieces, although stated 10,000

03. 25 Steloj (.983 Gold, Weight: 50.0 g, Diameter: 37.8 mm, Plain Edge with numbered with a mintage of 10 pieces)