An important update to make this thread up to date.

The Guild took part of GraphQL Mesh and turned it into a GraphQL gateway called Hive Gateway - here's a blog post about it.

GraphQL Mesh is now using GraphQL Federation under the hood to compose different APIs (gRPC, OpenAPI, Swagger, databases etc.) into a Supergraph served by Hive Gateway.

Right now the difference between GraphQL Mesh and Apollo Federation is that GraphQL Mesh turns any API into GraphQL that can be served as Apollo Federation subgraph. In short, GraphQL Mesh extends Apollo Federation, it takes it to the next level.