Oracle Database 10g Express (Oracle Database XE)
Oracle is a newcomer to the Open Source database market, as they only provided commercial database packages until recently. The Express edition is a response to free competitors in the open source market, and it provides a method for marketing their flagship commercial database product.
The express edition is a scaled-down version Oracle database with a small size based on the 10g Release. Like other open source products, it is free to use for development, installation and distribution. It is also vastly simpler to administer than a fully blown commercial version of 10g usually seen in an enterprise environment.
Oracle points out that their Express product is a good starting point for PHP, Java, .NET, XML and other open source technology developers. For DBAs, it is a good training environment to increase skills and to use for deployment experience.
Commercially, it can also be used by small software suppliers and other companies requiring a starter database to use to run their business. It is also widely used in educational institutions.
The Oracle Express product can be installed on a number of different platforms, but they do point out that the resources needed for the express version can be heavy such as the need to provide for storage of up to 4GB for user data, and 1GB of memory.
However, Oracle Express is widely supported with a community of experienced and inexperienced users of Oracle alike, and the community also has the benefit that professionals from commercial Oracle environments can also assist with familiar problems.