In 2008, Sun purchased MySQL for a reported $1 billion (US) and Sun has since been purchased by Oracle. Monty Widenius, the original creator of MySQL, has since left Sun, apparently over philosophical differences. In particular there seems to be a difference of opinion when it comes to the appropriateness of the 5.1 release of MySQL (i.e., was it too buggy for public release). Widenius is now working on MariaDB, an offshoot of MySQL that uses the Maria storage engine (aka table type) by default. This is definitely a project to keep an eye on, as MySQL users will logically move to MariaDB if they do find MySQL to be increasingly unstable or they just disagree with how Sun/Oracle is managing the product. As with many things, the popularity of MariaDB will partially depend upon the adoption rates by hosting companies. Or, for those that do stick with MySQL, version 6 will include support for the Maria storage engine. See this page for more on MariaDB compared with MySQL.
The intention behind MariaDB is to release free and stable, but very similar, alternative to MySQL. The Maria storage engine is a crash-safe version of the MyISAM table type but Maria still doesn’t use transactions (like InnoDB). Version 1.5 of MariaDB is now in beta, with the focus on stability. Version 2 of Maria should include transactions and ACID compliance. Version 2.5 is where the developes intend to really focus on performance. This may seem a little backwards, but it’s much easier to retroactively improve software performance than it is its quality.