The US equivalence is the Freedom of Information Act, but it's better not to use that parallel, because all US citizens will only get the wrong impression. The rule is from the 15th century, and is of course no oddity at all.
Most legal systems state the same.
The offentlighetsprincip is part of the constitution of the Kingdom of Sweden. There is of course also elaborate rules, a thick law, when public papers must be classified. But the basic principles from 1766 have never been changed. And when the computers came, data information became as public as information on paper. The offenlighetsprincip is truly revered.