There is no clear definition of what a frame implementation is. As a first approximation, a frame can be thought of as an extension of the Lisp property list. Numerous frame-like software packages have been developed, including FRL, KRL, KL-ONE.
Object-oriented languages can be considered to belong to the class of frame languages; CLOS (Common Lisp Object System) is provided in Common Lisp. These languages trace their ancestry to the simulation programming language Simula. Smalltalk is a ``pure'' object-oriented language.