PostgreSQL is a robust relational database system with over 25 years of active development that runs on all major operating systems. It is fully ACID compliant, and 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, and ODBC, among others, and exceptional documentation.
MUSCLE (Multi User Server Client Linking Environment) is an N-way messaging server and networking API. It includes client-side networking APIs for various languages, including C, C++, C#, Delphi, Java, and Python. MUSCLE lets programs communicate over a network via streams of serialized Message objects. The included server program ("muscled") lets its clients message each other and store information in its server-side hierarchical database. The database supports flexible queries via hierarchical wildcarding, and "live" updates via a subscription mechanism.
BaseX is a light-weight, high-performance, and scalable XML database system and XPath/XQuery processor, including full support for the W3C Update and Full Text extensions. An interactive and user-friendly GUI frontend gives you great insight into large XML data instances. It is platform independent and works out of the box.
PostGIS adds support for geographic objects to the PostgreSQL object-relational database. In effect, PostGIS "spatially enables" the PostgreSQL server, allowing it to be used as a backend spatial database for geographic information systems (GIS), much like ESRI's SDE or Oracle's Spatial extension.
hamsterdb Embedded Storage is an embedded database engine written in ANSI-C. It includes B+Trees with variable length keys and records. It supports in-memory databases and endian-independent files, database cursors, multiple databases in one file, "record number" databases, and duplicate keys. hamsterdb is very fast and highly configurable. It compiles and runs on Unix platforms, Linux, Microsoft Windows, and Windows CE.
db4o is an object database for Java and all .NET environments. Its features include ACID transactions, automatic class schema recognition, query-by-example, a S.O.D.A. object querying API, native queries, LINQ support on .NET, callback methods, memory files, cascade-on-delete, multi-threaded access, and Java Webstart and servlet support.
The unixODBC project provides Unix applications with the same ODBC 3.51 API and facilities available under Windows. It provides a Driver Manager that supports the full ODBC API and performs the ODBC 3 to ODBC 2 translations with UNICODE to ANSI conversion. It also includes a set of graphical utilities that allow users to specify connections to DBMSes to be used by applications, a collection of ODBC drivers including a simple text based driver, an NNTP driver, a Postgres driver and others, and a selection of templates and libraries that to aid in the construction of ODBC drivers. It works with MySQL, Postgres, StarOffice/OpenOffice, Applixware, iHTML, PHP, Perl DBD::ODBC, and many other applications and drivers. Connection pooling is also provided to increase performance with applications such as PHP.