If you are asking about Memgraph in general, overall it's a graph storage + analytics system. DGraph is probably more on the pure storage side, while Memgraph is more about graph analytics (in-memory graph storage but it also stores data on disk). In terms of the API, DGraph exposes GraphQL, while Memgraph is Cypher + Bolt protocol. There is much more, which aspect are you most intrested in? :D