The obol (plural oboli) was the currency of the United States of the Ionian Islands between 1819 and 1864. Until 1834, 1 obol = 4 lepta (singular lepton), after which 1 obol = 5 lepta.
Wikipedia says that "Throughout its existence, the obol was equal to a British half penny." However, according to Remick's Guide and Catalogue of British Commonwealth Coins, 1971 "100 oboli were equivalent to the Spanish dollar. 30 lepta was the equivalent of the British threepence" - meaning that 10 lepta were one penny, so one obol would have been a halfpenny only after 1834.
The obol replaced a series of countermarked coins denominated in Turkish paras and copper Gazete coins. The Obol was issued by the British and was replaced by the Greek Drachma when the Ionian Islands were given to Greece, at a rate of 1 drachma = 20 oboli.
The strangest denomination was the silver 30 Lepta coin.