DocumentDB

DocumentDB is a fully managed non-relational document database, with full MongoDb compatibility, that means it is very useful for JSON data, it is able to scale automatically up to 64TB.

Cluster endpoint - for apps that require both read and write -access to the database

Reader endpoint: used to connect to read replicas

Instance Endpoint: every instance within your cluster, including your primary and read replica instances, will each have their own unique instance endpoint that will point to itself. Useful for load-balancing reasons.

Keyspaces ( for Cassandra )

Keyspaces is scalable fully managed Apache Cassandra compatible database service (serverless), which allows you to use the CQL (Cassandra Query Language).

Cassandra is a free and open-source distributed, wide column store, NoSQL database management system.

A Keyspace is basically a group of Tables, Tables are where you write data to. Similarly to DynamoDB you can define Provisioned or On-Demand Capacity Modes.

Neptune

Neptune is a fully managed graph database service, its use cases are for fraud detection, recommendation engines, social networks and applications that use open source APIs like Gremlin, openCypher and SPARQL.

Like DocumentDB, it has Cluster, Reader and Instance Endpoints

QLDB

Quantum Ledger Database

QLDB is a fully managed , serverless, ledger database for transparent immutable and cryptographically verified transaction log.

Data can be only appended ( no overwrite or deletion ) to journals therefore QLDB is great when Integrity Assurance is required.