Here’s a quick overview of the managed database services offered by Amazon:

RDS (Relational Database Service): Service allows selection of one of these relational database engines: Aurora (Amazon’s engine), MariaDB, MySQL, Oracle, PostgreSQL, SQL Server. RDS allows you to set up read-only replicas, as well as multi-AZ (Availability Zone) deployments.
Aurora is Amazon’s proprietary database engine. You select either MySQL or PostgreSQL compatibility. Aurora also has a serverless version, as well as Global Database for cross-region read-only replicas.

DocumentDB: JSON document database with MongoDB compatibility.

DynamoDB: Key-Value store.

ElastiCache: Caching with Redis and Memcached compatibility.
MemoryDB: Redis compatible with durable storage.

Keyspaces: Column family DB with Cassandra compatibility.

Neptune: Graph database that supports Gremlin and SPARQL query languages.

QLDB (Quantum Ledger DataBase): Ledger database – I’ve written on QLDB earlier.

Redshift: Data warehouse service

Timestream: Time Series database.