In Scheme, as in other Lisp dialects, “everything is an object”. But Scheme is not “object-oriented” in the sense of classes and methods.
Various Scheme implementations have bolted an object system on top of standard Scheme. Most of these are variants of the Common Lisp Object System (CLOS) which evolved from an older Lisp Machine object system called Flavors. The Kawa and IronScheme implementations have Java and C# style object systems, respectively.
Included since 1.9. Mainly inspired by Meroon.