Mongoose
Node.js ODM (Object Document Mapper) for MongoDB. Aaron Heckmann, 2010. Adds schema validation + middleware on top of MongoDB's schemaless nature.
Even though MongoDB is "schemaless", people usually want schema consistency — Mongoose provides it. Supports hooks (pre/post save), virtuals, populate (join-like), plugins. Competitors: Prisma (type-safe, multi-database), TypeORM, Drizzle (for SQL), MongoDB native driver (lighter, less magic). Modern trend: bypass Mongoose, use TypeScript + MongoDB Schema Validation. Maintained since ~2018 by Valeri Karpov (LearnSomething/MeanIT).