The story
The Czechoslovak koruna (crown) was a soft currency, that is, not exchangeable for other currencies outside the country. In 1948, shops were established under the name Darex to sell goods to foreigners for foreign (hard) currency only (based on the earlier Torgsin shops in the Soviet Union). Later, these became open to ordinary citizens, but not for crowns. In 1950, to speed up transactions and limit fraud, foreign currency was first converted into Darex vouchers in values of crowns.
In 1957, the PZO (Foreign Trade Enterprise) Tuzex (a contraction of tuzemský export [domestic export]) was founded in order to get convertible foreign currency into the country. This currency came directly from foreigners visiting the country, but also from relatives or citizens working abroad, who could send currency to friends and family to buy items in Tuzex, with Tuzex vouchers instead of Darex ones. The vouchers could not be re-exchanged for foreign currency and were valid for a limited time. (The state would convert unused vouchers back to normal currency at a rate of 2 crowns per Tuzex crown, a fraction of their effective purchasing power.)
The first shop was established in Prague on Rytířská street, and the next in Bratislava. In 1961 there were 14 shops, rising to 170 in 1988.
However, the fact that otherwise unavailable luxuries could be purchased led to an unofficial or grey market (technically illegal but tolerated) buying Tuzex vouchers with Czechoslovak currency at a high premium, typically 5 to 1. The Darex and Tuzex vouchers were colloquially known as bony. The hustlers or spivs who would offer sell them on the street (close to a Tuzex shop) were known as veksláci (from German Wechsel - exchange) A 1987 film with title: Bony a klid (vouchers and tranquility as a (phonetical) reference to Bonnie and Clyde) reflects the daily lives of petty criminals dealing with the vouchers.
Following the Velvet Revolution in 1989 and the reformation of the country, citizens were able to travel abroad more freely and to legally deal with other currencies. In addition, improved domestic economy and more imports meant that Tuzex sales declined. The sale of Tuzex vouchers ceased on 30 June 1992.
As well as running the shops, the Tuzex corporation had activities in various countries in order to trade Czechoslovak goods and obtain supplies for the shops. This continued for a while after the closure of the shops in 1992 to complete contracts and for liquidation of the assets.
From Wikipedia’s article on Tuzex, shared under CC BY-SA 4.0.4