The document compares several meta-metamodeling languages including ARIS, Ecore, GOPPRR, GME, MS DSL Tools, and MS Visio. It finds that while object type, relation type, and attribute are core concepts supported by all languages, relation types can be realized in different ways. The analysis also observes some languages like GOPPRR and GME have greater practical expressiveness while others such as Visio are more limited. Future work could improve the comparison criteria, include more meta-metamodeling languages, and study model interoperability through transformations between meta-modeling concepts.