MongoDB Atlas Vector Search and Neo4j are two prominent databases with vector search capabilities, essential for recommendation engines, image retrieval, and semantic search in AI-driven applications. Both use the Hierarchical Navigable Small World (HNSW) algorithm for indexing and searching vector data. MongoDB Atlas Vector Search is built into its document-based architecture, while Neo4j has vector search built into its graph structure. The choice between them depends on factors such as data model, application requirements, scaling needs, and integration preferences.