The Game Ontology Project (GOP) is a framework for describing, analyzing and studying games. It is a hierarchy of concepts abstracted from an analysis of many specific games. GOP borrows concepts and methods from prototype theory as well as grounded theory to achieve a framework that is always growing and changing as new games are analyzed or particular research questions are explored. Further details are available here (pdf).
The GOP originally began in 2002 as the Game Morphology Project led by Janet Murray at Georgia Institute of Technology. Starting in 2003 it was been led by Michael Mateas and Jose Zagal with the participation of various members of the Experimental Game Lab. The GoP currently resides at DePaul University's College of Computing and Digital Media under the leadership of Jose Zagal.