An open source database
Edit By BS Editor: MySQL - Multi-user and robust SQL database server. The worlds most popular open source database
MySQL is a very fast, multi-user, multi-threaded and robust SQL (Structured Query Language) database server. The worlds most popular open source database.
MySQL is an attractive alternative to higher-cost, more complex database technology. Its award-winning speed, scalability and reliability make it the right choice for corporate IT departments, Web developers and packaged software vendors

Features:

A broad subset of ANSI SQL 99, as well as extensions
Cross-platform support
Stored procedures
Triggers
Cursors
updatable Views
True VARCHAR support
INFORMATION_SCHEMA
Strict mode
X/Open XA distributed transaction processing (DTP) support; two phase commit as part of this, using Oracles innodb engine
Independent storage engines (MyISAM for read speed, InnoDB for transactions and referential integrity, Archive for storing historical data in little space)
Transactions with the InnoDB, BDB and Cluster storage engines; savepoints with InnoDB
SSL support
Query caching
Sub-SELECTs (i.e. nested SELECTs)
Replication with one master per slave, many slaves per master, no automatic support for multiple masters per slave.
Full-text indexing and searching using MyISAM engine
Embedded database library
Full Unicode support
Acid compliance using the InnoDB, BDB and Cluster engines
Shared-nothing clustering through MySQL Cluster you can free download MySQL 5.1.22 RC now.