Redis

PostgreSQL, also known as Postgres, is a powerful, open-source object-relational database system. It emphasizes extensibility and SQL compliance, offering advanced features like complex queries, foreign keys, triggers, and transactional integrity. PostgreSQL is known for its reliability, data integrity, and ability to handle complex workloads. Its support for both relational and non-relational querying makes it versatile for various applications. PostgreSQL's robust feature set and active community make it popular among developers and organizations requiring a sophisticated, scalable database solution.

MongoDB is a document-oriented NoSQL database used for high volume data storage and complex applications. It stores data in flexible, JSON-like documents, allowing for dynamic schemas and easy scalability. MongoDB offers features like automatic sharding, replication for high availability, and a powerful query language. Its ability to handle large volumes of unstructured data and its scalability make it popular for big data applications, content management systems, and real-time analytics. MongoDB's flexibility and ease of use contribute to its widespread adoption in modern application development.

MariaDB is an open-source relational database management system that is a fork of MySQL. It's designed to be a drop-in replacement for MySQL with more features, new storage engines, and improved performance. MariaDB offers features like advanced clustering with Galera Cluster, more storage engines, and better performance optimizations. Its commitment to remaining open-source and its compatibility with MySQL make it an attractive option for organizations looking for a powerful, community-driven database solution.

Percona server is an opensource, fully compatible, enhanced drop-in replacement for MySQL, providing superior performance, scalability, and instrumentation.

Solr is an open-source enterprise-search platform, written in Java.