Can you name and explain popular non-relational data storage systems?

Popular NoSQL data storage systems include:

• MongoDB — a document-oriented database where data is stored in JSON-like documents. Suitable for flexible schemas and rapid prototyping.

• Redis — an in-memory key-value store, often used for caching and fast data access.

• Cassandra — a distributed columnar database optimized for handling large volumes of data with high availability.

• Neo4j — a graph database designed for storing and processing data with relationships, such as social networks.

Each of these systems differs in data model and use cases, allowing for the selection of the optimal solution for specific tasks.