This document provides an overview of NoSQL databases. It begins with an assessment of relational databases, noting their advantages like normalization but also limitations like handling data changes. It then discusses the rise of NoSQL databases, noting some points of convergence but also significant disparities between products. It focuses on Redis, Cassandra, MongoDB, and Neo4j, describing their data models, querying capabilities, and additional features like replication. The conclusion is that not all problems require a relational solution.