MySQL
is a very fast, multi-threaded, multi-user and robust SQL (Structured Query Language) relational database server. MySQL is Free software. It is licensed under the GNU General Public License.
MySQL is open source and works on many different platforms including AIX, BSDi?, [DEC Unix]?, FreeBSD, HP-UX?, Linux, Mac OS X, NetBSD, OpenBSD, OS/2 Warp, SGI Irix, Solaris, SunOS, SCO OpenServer?, SCO UnixWare?, [Tru64 Unix]?, Windows 95, 98, NT and 2000.
MySQL has C, C++, Eiffel, Java, Perl, PHP, Python, and Tcl APIs.
In case you were wondering MySQL is pronounced My S-Q-L NOT My-Sequel.