Open Source

Arboretum Metric Access Method Library
GBDI Arboretum is a portable C++ library which implements various Metric Access Method (MAM). By using this library applications will be able to perform similarity queries (queries by contents).
http://gbdi.icmc.usp.br/arboretum/

ART
A lightweight (Java/J2EE), multiplatform web based query tool and reporting environment. Supports tabular, crosstab, charts, scheduling; data exportable to spreadsheet.
http://art.sourceforge.net

Axamol SQL Library
Java library to execute SQL statements stored in external library files. This separation increases readability, eases maintenance, and allows separate testing and documentation. [MIT]
http://www.slamb.org/projects/axamol/sql-library/

BFMP Project
Open-source business template for Filemaker Pro 9.0 that supports sales, inventory, quotes, and taxes, in multiple languages for multiple users.
http://bfmpproject.webs.com/

Bond
A Linux rapid application development (RAD) tool for creating dynamic data aware database applications from standard design specifications.
http://www.treshna.com/bond/

ChurchInfo Church Database Application
ChurchInfo is a php/mySQL database to keep track of people, families, groups, pledges and payments, Sunday school classes, etc.
http://www.churchdb.org

Clip
Object oriented, CA-Clipper and Xbase compatible compiler.
http://www.english.itk.ru/clipper/index.html

CQL++
Both a single user and client/server versions with ODBC drivers. Distributed under a modified GPL that allows distribution of applications without including source code. Commercial support available.
http://www.cql.com/

Fast DB
Main memory object-relational DBMS featuring log-less transaction recovery, tight C++ integration, query language like SQL. Optimized for all data being held in RAM.
http://www.geocities.com/SiliconValley/Orchard/5802/fastdb.html

Hamsterdb Embeddable Database Engine
Hamsterdb is written in ANSI C and supports a B+Tree index structure, uses memory mapped I/O (if available), supports cursors, and can create in-memory databases.
http://www.hamsterdb.com

Index of Publicly Available Database Software
A list of research and other free database systems. Also includes some benchmarks. Maintained by ACM SIGMOD.
http://www.sigmod.org/databaseSoftware/

iSQL-VIewer
An SQL browser tool that works with any JDBC 2.0 or higher driver. [Open Source, MPL]
http://isql.sourceforge.net/

ITTIA
Provides small footprint, high performance, and easy-to-use embedded database solutions. Also sells technical support and consulting.
http://www.ittia.com/

JavuSQL
Small embedded relational database. Complete Java RDBMS in JDBC driver. Based on SQL-92 [LGPL].
http://www.programics.com/?page=javusql

Kexi
An integrated environment for managing data. It helps creating database schemas, inserting, querying and processing data. Screenshots, downloads, resources, a wiki and a list of involved developers.
http://www.kexi-project.org/

Mneson
Pure Ada database including library and tools for persistent graphs of basic values (integer, string, float).
http://www.liaad.up.pt/~maa/mneson/

MonetDB
Open source high-performance database system developed at CWI, the Institute for Mathematics and Computer Science Research of The Netherlands.
http://monetdb.cwi.nl/

MyOODB ( My Object-Oriented Database & Web Services )
An Object-Oriented Database and Web Services (SDK) written in Java, includes documentation, example code and information about the author.
http://www.myoodb.org

Ocelot Computer Services Inc.
The Ocelot SQL DBMS adheres closely to the ANSI/ISO SQL standard. The site has software downloads, tutorial information, and reviews of SQL or general DBMS books. [Mozilla and GPL]
http://www.ocelot.ca

One$DB: Open Source Database
Free and open source version of Java database Daffodil DB. Available in both network and embedded editions.
http://www.daffodildb.com/one-dollar-db.html

OSDB: The Open Source Database Network
News, information, and tools related to open source database platforms.
http://osdb.org

Persistent Data Objects
A flexible, lightweight object oriented database system in C++ with an extensible back-end store design. MFC compatible version available. [GPL]
http://www.geocities.com/brianleeprice/pdo.html

picoSQL
picoSQL is a SQL-based, multi-user, client/server RDBMS, derived from a commercial project [GPL].
http://www.picosoft.it/picosql/

Qt SQL Browser
A graphical front end for any ODBC compliant database [GPL]
http://www.mobiustech.net/qtsql/

RekallRevealed
Rekall is an open source database front end, in the style of Microsoft Access. It is built on Qt and KDE and runs on Linux and Windows. Open source drivers available for MySQL, PgSQL and XBase (DB4 via a wrapper library) [GPL]
http://www.rekallrevealed.org

Seva Software - ArunaDB
Database server written in Ruby that supports tables, indexes, triggers, sequences, views, stored procedures, and transactions.
http://sevainc.com/arunadb.html

The TDB Replication System
An open source suite of software that provides a high-performance, replicated, distributed peer-to-peer Unix DBM style database built on TDB.
http://tdbrepl.inodes.org

tdbengine - The turbo database engine
tdbengine is a small but powerful RDBMS written in PASCAL. It runs on Linux as well as on Windows machines.
http://www.tdbengine.org