The MySQL database has become the world's most popular open source database because of its high performance, high reliability and ease of use. It is also the database of choice for a new generation of applications built on the LAMP stack (Linux, Apache, MySQL, PHP / Perl / Python.) Many of the world's largest and fastest-growing organizations including Facebook, Google, Adobe, Alcatel Lucent and Zappos rely on MySQL to save time and money powering their high-volume Web sites, business-critical systems and packaged software.
MySQL runs on more than 20 platforms including Linux, Windows, Mac OS, Solaris, IBM AIX, giving you the kind of flexibility that puts you in control. Whether you're new to database technology or an experienced developer or DBA, MySQL offers a comprehensive range of database tools, support, training and consulting services to make you successful.
MySQL used to be abysmal in its early versions, barely worthy of the name "relational database". Table corruption and missing essential SQL and relational features were rampant. These days they do have caught up, but I still prefer the power and purity of Postgres. For PHP users this probably still is the easiest and most simple to setup database though.