Oracle Database!

MySQL Community Edition is a freely downloadable version of the world's most popular open source database that is supported by an active community of open source developers and enthusiasts.

MongoDB (from "humongous") is a scalable, high-performance, open source NoSQL database. The database is document-oriented so it manages collections of JSON-like documents. Many applications can thus model data in a more natural way, as data can be nested in complex hierarchies and still be query-able and indexable.

Tibero provides enterprise performance and scalability, database reliability through clustering, improved data security through stronger keys and expanded encryption. Tibero is easy to port though automatic conversion tool from existing Oracle databases with little to no change required to existing PL/SQL or applications. It is also half of Oracle’s license and support costs that results in a very low TCO compared with Oracle.

RethinkDB pushes JSON to your apps in realtime.

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 overall cost of ownership.

Database .NET is an innovative, powerful and intuitive multiple database management tool.With it you can Browse objects, Design tables, Edit rows, Export data and run Queries with a consistent interface. A standalone tool that does not require installation.

Cockroach is a distributed key/value datastore which supports ACID transactional semantics and versioned values as first-class features. The primary design goal is global consistency and survivability, hence the name. Cockroach aims to tolerate disk, machine, rack, and even datacenter failures with minimal latency disruption and no manual intervention. Cockroach nodes are symmetric; a design goal is one binary with minimal configuration and no required auxiliary services.

H2 is a relational database management system written in Java. It can be embedded in Java applications or run in the client-server mode. The disk footprint (size of the jar file) is about 1 MB.

MemSQL is a next generation database that removes the most common bottleneck most applications hit today: disk. By offering a familiar relational interface to an in-memory data tier, MemSQL empowers developers with the technology web-scale companies use to cope with massive traffic and growth. MemSQL offers orders of magnitude improvements in write and read performance and greatly simplifies application development and maintenance.

HBase is an open source, non-relational, distributed database modeled after Google's BigTable and is written in Java. It is developed as part of Apache Software Foundation's Apache Hadoop project and runs on top of HDFS (Hadoop Distributed Filesystem), providing BigTable-like capabilities for Hadoop. That is, it provides a fault-tolerant way of storing large quantities of sparse data.

CUBRID is a comprehensive GPL/BSD open source relational database management system highly optimized for Web Applications. CUBRID is being developed in C/C++. Includes native HA, online hot backup, and other features. JDBC, PHP, ODBC/.NET, Ruby & Python APIs.

DB2 offers industry leading performance, scale, and reliability on your choice of platform from Linux to z/OS. DB2 supports storing XML and relational data and offers SQL PL and PL/SQL procedural languages.