Neo4j is a popular graph database that has been used by Jim Weaver for his project, which combines Wikidata and Wikipedia to create a semantic navigation system. The use of Neo4j allows for fast querying and storage of large amounts of data, with 11 million nodes and 74 million relationships. Weaver attributes the choice of Neo4j to its Java compatibility and performance, as well as its growing popularity among developers. He has found Neo4j to be a powerful tool for solving real-world problems, with impressive speed and simplicity in querying and importing data. If he could go back in time, Weaver would take advantage of the latest features and tools available in Neo4j 3.0 to streamline his project's data import process.