SQLite is a software library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine. SQLite is the most widely deployed SQL database engine in the world. The source code for SQLite is in the public domain.
PostgreSQL is a powerful, open source object-relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness.
Redis™ (REmote DIctionary Server) is an open-source, networked, in-memory, key-value data store with optional durability. It is often referred to as a data structure server since keys can contain strings, hashes, lists, sets and sorted sets.
SQL Server delivers on Microsoft’s Data Platform vision by helping your organization manage your data by enabling you to store data from structured, semi-structured, and unstructured documents within the database.
Apache CouchDB is a distributed, fault-tolerant and schema-free document-oriented database accessible via a RESTful HTTP / JSON API. It includes incremental map / reduce mechanics for queries and keeps data safe with an append-only datastore.
Apache Cassandra has become the leading NoSQL platform driving many of today's modern business applications by offering continuous availability, high scalability and performance, strong security, and operational simplicity while lowering the overall cost of ownership.