Aside from numerous (mainly British) dependencies that recognise the local currency as well as the mother state's (e.g. the Channel Islands each have their own pound as well as the British one), there are a number of independent countries that recognise two or more currencies at once, as shown at https://en.wikipedia.org/wiki/List_of_circulating_currencies
. Examples include Brunei and Singapore recognising each other's dollars, the South African rand being accepted together with the local dollar in Namibia and loti in Lesotho, and the current prize winner, Zimbabwe, which accepts the Botswana pula, British pound, Euro, South African rand,
United States dollar, and Zimbabwean dollar. Zimbabwe's own very weak currency situation gives an example of what led several states to abandon their own currency altogether, adopting another country's "stronger" currency- e.g. Ecuador, East Timor.
Several independent countries (Pacific islands) use the Australian (or US or NZ) dollar in commerce, but mint their own currencies commemoratively, like Kiribati, Nauru and Tuvalu.
Cambodia has just one currency, the riel.