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.
OpenLink Virtuoso is a scalable, high-performance SQL-200n compliant object-relational database engine. It provide sophisticated database management for SQL, XML, and RDF. All interaction with Virtuoso occurs via its support of industry standard query languages, protocols, APIs, and data formats such as: ODBC, JDBC, OLE-DB, ADO.NET, XMLA, SQL, SPARQL, XQuery, SOAP, HTTP, WebDAV, SyncML, Atom (Publishing and Syndication), RSS, RDF, and more.
KInterbasDB is a Python extension package that implements Python Database API 2.0-compliant support for the open source relational database Firebird and some versions of its proprietary cousin Borland Interbase. In addition to the minimal feature set of the standard Python DB API, KInterbasDB also exposes nearly the entire native client API of the database engine.
Daffodil DB is a SQL-99 specification compliant, lightweight, Java-based relational database engine (RDBMS). It supports almost all constructs of SQL 99 (including triggers, views, constraints, UDT, stored procedures, etc.), supports distributed transactions (XA), provides a complete JDBC 3.0 driver (including support for optional features like save points, rowsets, UDT, XA, connection pooling, etc.), and can run in embedded or server mode. It can be included as a jar file in any Java application. Daffodil DB includes Daffodil DB Browser, a GUI-based database management tool that can be used to carry out all database operations such as creating a database, creating database objects, executing SQL statements, and manipulating data, browser database objects, etc.
php_db2util is a module that extends PHP with mass data movement functions. It supports connecting to a DB2 server, loading data from a client or server with a replace option or insert option, and exporting data from a table to a client. It also allows the runstats utility to be run to recreate indexes.
TwinDB is an embedded key/value database based on BerkeleyDB. It basically adds security from database corruption on top of the non-transactional version of BerkeleyDB. It accomplishes this by maintaining twin BerkeleyDB databases and using "lock" files to indicate when a set of writes are in progress. Performance is still good (tested at ~60K writes/sec and 300K reads/sec). It was written because the transactional version of BerkeleyDB is expensive.
SQLite/Ruby is a set of bindings to allow the SQLite (v 2.x) database to be used from Ruby scripts. It provides an object-oriented interface to all major functions of the SQLite API, including the create_function and create_aggregate functions. It also supports bind parameters, transactions, internal and external iterators, type translation in queries, and easy access to various pragmas.