"Databases were once the forgotten stepchild of the
open-source family. Companies like Red Hat Inc. included database
software with their Linux distribution disks, but the main focus
was on the operating system, the kernel and the graphical
interface. A database was just another add-on, like a Minesweeper
clone. But now, companies and users are scrambling to realize the
value locked up in quality, open-source database software.
The two major open-source databases are MySQL, a lightning-quick
database with roots in Sweden, and PostgreSQL, the latest version
of a venerable database project (Postgres) that began at the
University of California, Berkeley. Both are common programs that
are installed on many servers and are often included free with
other packages and distributions. Other versions and cousins exist
for different markets. Lincoln, Mass.-based Sleepycat Software
Inc., for instance, builds and maintains a small database, which it
calls Berkeley DB, for embedded systems.
...Finding high-profile open-source database users isn't hard.
Many Web sites, including Yahoo and Slashdot, depend upon
open-source databases like MySQL to store articles and comments.
Many companies that provide shared servers now offer MySQL
databases as an inexpensive option, practically guaranteeing that
many low-budget Web sites depend upon the tools."