Ingres is a feature rich and robust database (RDBMS) that's free to use, modify, and redistribute. Support is available for a reasonable price if you need it. Ingres supports many programming languages, including Python, Ruby, Java, Perl, C/C++, and more. Ingres has a bit of a learning curve, but once mastered is extremely powerful and highly tunable. It is also very stable and reliable. Ingres is one of a fairly small number of databases providing excellent geospatial features including data types and functions compliant with the Open Geospatial Consortium (OGC) Simple Feature Specification (SFS) for SQL.
MariaDB is a database server that offers drop-in replacement functionality for MySQL. It is built by some of the original authors of MySQL, with assistance from the broader community. In addition to the core functionality of MySQL, it offers a rich set of feature enhancements including alternate storage engines, server optimizations, and patches.
NNDB is a C++ library that provides in-memory data storage and retrieval using syntax that is intended to feel natural for C++/STL, but which also might feel slightly like SQL if you squint and pound the top of your head with a seminal programming textbook. Columns types are fixed at compile-time and checked by the compiler.
Nextls is a console application that keeps track of your music collection using a MySQL database to store information such as length, bitrate, metadata, and where on the hard drive it is located. When Nextls is launched, it will figure out any changes done since the previous run and update the database accordingly. The database is very simple to work with, and there also exists a sister project in Nx2 that will allow you to take your database online and stream your music from a Web browser.
TYPO3 CMS is a Web Content Management System which features automatic creation of navigational menus, headlines, and other dynamic graphical elements, automatic conversion and scaling of images, the ability to present different templates based on variables such as client browser or country code, support for multiple templates on a site, and a built-in password-protection option. Pages can be timed to be shown on a certain date, be hidden on a certain date or just temporarily hidden. TYPO3 supports search in SQL-databases and redesigning of a website at once is just a matter of creating a single new template.
libubiqx is an in-memory database suitable for use in embedded systems. The libubiqx database management system is a fully functional DBMS API that supports both hierarchical and relational data architectures. It provides developers with robust and scalable data management tools for use in embedded systems or SNMP agent applications.