Flora is a minimalistic but very powerful NoSQL database. It is easy to understand with data readable by both humans and machines, schemaless, Lua-scriptable, remotely accessible through TCP, and portable. It is especially suited for A. I. tasks, and a longer-term goal is support for "natural language" queries.
The NCBI C++ Toolkit provides portable libraries and applications for assisting genetic science. These include libraries for networking, SQL and BerkeleyDB access, CGI and HTML handling, ASN.1 and XML handling, sequence alignment engines, sequence retrieval engines, BLAST database engines, FLTK and OpenGL graphics toolkits, and basic system utilities.
MP3DB2 is a collection of bash scripts for keeping track of large MP3 collections. It will retrieve song information from the filenames and ID3 tags of a directory or CD of MP3s and store them in a local database. It then allows you to search any of the fields, generate a master listing of all your complete albums, see the size of your entire collection, and more.
SQLite is a small, fast, embeddable SQL database engine that supports most of SQL92, including transactions with atomic commit and rollback, subqueries, compound queries, triggers, and views. A complete database is stored in a single cross-platform disk file. The native C/C++ API is simple and easy to use. Bindings for other languages are also available.
PersistClass provides access to relational databases for PHP. It attempts to focus on simplicity and convenience by eliminating the need for boilerplate, meaningless code. It can establish database connections (MySQL, Oracle, etc.), execute SQL queries, parse query results, provide convenience methods (read a single row or value, etc.), escape data (against SQL injection, HTML escaping for outputs), handle transactions, and provide strict error handling and object persistence (storing and retrieving PHP objects in db tables).