PostgreSQL is the most capable Open Source database server available, with functionality that can complete or even exceed proprietary SQL database products.
Setting up MySQL remote access with SSL encryption is surprisingly awkward. This article describes all of the steps that are necessary to make this feature work in practice.
Apache Derby (or Java DB) provides a small set of libraries that can be added directly to any Java program that needs database storage capabilities, such as a desktop application, network service, or Web application.
MySQL provides all of the essential functionality required for a SQL database service. Although it is most frequently used to provide data storage for Web applications on the same system, MySQL supports replication and clustering across networks.