DMtools
A data mining toolbox with caching of database queries and parallelism within a collection of independent queries. [Open Source, GPL]
http://datamining.anu.edu.au/software/dmtools/

Lexxe
Processes natural language queries and delivers results in clusters by topic. Queries can be keywords, phrases or short questions.
http://www.lexxe.com/

dBOrganiser
Easily manage the objects contained in a database. Tables and queries (if the database supports queries) for two databases are displayed alongside each other, in a split screen.
http://chiselsoftware.com/dborganiser/

A free cookbook for sql queries
This is a free repository for SQL queries and examples as well as database related articles
http://www.sqlrecipes.com/

LDB
LDB is a free object-oriented database management system built on top of SHORE 2.0. It supports ODMG ODL specifications and can handle most ODMG OQL queries using a query optimizer. [Open Source but copyrighted]
http://lambda.uta.edu/ldb/doc/

DMTools
Written in Python, the toolbox handles caching of database queries and parallelism within a collection of independent queries. Our toolbox provides a number of routines for basic data mining tasks on top of which the user can add more functions - mainly domain and data collection dependent - for complex and time consuming data mining tasks. GNU/GPL. From the Computer Sciences Laboratory of The Australian National University
http://cslab.anu.edu.au/ml/dm/dm_software.html

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/

A.I.M.S. Drawing Management
Drawing-register software for use by construction companies. Includes automated drawing transmittals, reports, technical queries and instructions registers. Suitable for architect and engineer practices.
http://www.drawingmanager.co.uk/

RFKmap
A free code which join FastTemplate and PHPlib's class (DB_Sql) to create an object system for a content management and viewer. A easy syntax to create one instance to access a complex queries and mapping the results to a set of templates.
http://rfkmap.sourceforge.net/download/rfkmap.html

DB Solo
DB Solo - The SQL Query Tool
http://www.dbsolo.com/