MySQL, the world's most popular open source database.

PostgreSQL is a powerful, open source relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness. It runs on all major operating systems, including Linux, UNIX (AIX, BSD, HP-UX, SGI IRIX, Mac OS X, Solaris, Tru64), and Windows. It is fully ACID compliant, has full support for foreign keys, joins, views, triggers, and stored procedures (in multiple languages). It includes most SQL92 and SQL99 data types, including INTEGER, NUMERIC, BOOLEAN, CHAR, VARCHAR, DATE, INTERVAL, and TIMESTAMP. It also supports storage of binary large objects, including pictures, sounds, or video. It has native programming interfaces for C/C++, Java, .Net, Perl, Python, Ruby, Tcl, ODBC, among others

Firebird is a relational database offering many ANSI SQL-92 features that runs on Linux, Windows, and a variety of Unix platforms. Firebird offers excellent concurrency, high performance, and powerful language support for stored procedures and triggers. It has been used in production systems, under a variety of names since 1981. Firebird is a commercially independent project of C and C++ programmers, technical advisors and supporters developing and enhancing a multi-platform relational database management system based on the source code released by Inprise Corp (now known as Borland Software Corp) under the InterBase Public License v.1.0 on 25 July, 2000.

MaxDB is SAP’s own relational database system. You can use it in SAP solutions as a less expensive alternative to databases from other vendors.
MaxDB is included in the standard system under the NetWeaver Full Use License

FutureSQL is a Free, Open Source Rapid Application Development web database administration tool, written in Perl, using MySQL. It uses DBI:DBD and CGI.pm.
FutureSQL allows one to easily setup config files to view, edit, delete and otherwise process records from a MySQL database. It uses a data dictionary, configuration files and templates, and allows "pre-processing" and "post-processing" on both fields, records and operations.
It's very flexible and has a wide range of options. It can be used for administrative functions, but it can also be modified to allow web visitors to perform read only searches on data tables. It allows multiple setup files to provide different views or operations on the same data set. Thus, an administrator / programmer can tailor it to fulfill a large number of functions, providing a different look and feel for different web sites. Documentation is included in the setup file.

Kexi Project Homepage. Kexi is considered as a long awaited Open Source competitor for Microsoft Access, Filemaker and Oracle Forms.