The economic and monetary union of 15 European Countries is proposed to be made by 1999. But the currencies of two countries, Franc, have already the same value and circulate freely in both the countries. The countries are

Belgium and Luxembourg operated a long-standing monetary association under the Belgium–Luxembourg Economic Union, which fixed the parity between the Belgian franc and the Luxembourg franc and allowed mutual circulation and legal tender status of each other’s banknotes and coins in both countries. The fixed-parity arrangement (with a restored 1:1 parity after 1944 and confirmed in later years) and the practice of Belgian currency circulating in Luxembourg demonstrate that the two francs effectively had the same value and circulated freely between the two states until the euro replaced them [1].

Sources

1. [1] https://en.wikipedia.org/wiki/Belgium%E2%80%93Luxembourg_Economic_Union