Oreo O's was a cereal made by Post, that launched in 1998 and discontinued in 2007. It was still manufactured by the company Dongsuh in South Korea up until 2014 where it was discontinued due to concerns of E.Coli. Dongsuh resumed selling the cereal in 2016.
The cereal was re-released in June 2017 worldwide with it's original 1997 recipe. Although intially available as a Walmart exclusive, other grocery stores began selling it shortly after it's initial release.