Today at OMG a proposition has been made to going forward to a standardization of UML profile for Archimate. As such, it also acts as a bridge between the OMG and the Open Group.
ArchiMate is a visual modeling language for Enterprise Architecture.
Current implementations of UML profiles for that are provided by SparxSystems and Modelio. There is no formal metamodel for ArchiMate. However, a few seminal semi-formal metamodels are around in white papers. The idea is to have a RFC (Request For Comments) out in June 2014, based on an agreed upon UML profile.
The task is complex, also because there is some kind of relation with TOGAF (at a certain point in history this was true, then the two worlds diverged but there is still some overlap).