Berkeley DB (libdb) is a programmatic toolkit that provides embedded database support for both traditional and client/server applications. It includes b+tree, queue, extended linear hashing, fixed, and variable-length record access methods, transactions, locking, logging, shared memory caching, database recovery, and replication for highly available systems. DB supports C, C++, C#, Java, PHP, and Perl APIs. It supports key-value pair (NoSQL), SQL, and Java Object formatted data. It is available for a wide variety of Unix platforms as well as QNX, Android, Mac OS X, and several varieties of Windows.
Berkeley DB XML is a native XML database engine for use within your product. Made available as a C++ library with language bindings for Java, Perl, Python, PHP, and Tcl, it integrates directly into your application (it is not a standalone database server). It provides XQuery access into a database of document containers. XML documents are stored and indexed in their native format using Berkeley DB as the transactional database engine.
e4Graph is a C++ library that allows programs to store graph-like data persistently and to access and manipulate that data efficiently. With e4Graph, you can arrange your data in the most natural form that reflects the relationships between its parts, rather than having to force it into a table-like format. The e4Graph library also allows you to concentrate on the relationships you want to represent, and not on how to store them in a database. You can modify data items, and add and remove connections and relationships between pieces of data on the fly. e4Graph allows you to represent an unlimited number of different connections between pieces of data, and your program can selectively manipulate the data according to the relationships it cares about, not having to know about other connections represented in the data set.
Ellogon is a multi-lingual, cross-platform, general-purpose language engineering environment, developed in order to aid both researchers who are doing research in computational linguistics, as well as companies who produce and deliver language engineering systems. As a language engineering platform, it offers an extensive set of facilities, including tools for processing and visualising textual/HTML/XML data and associated linguistic information, support for lexical resources (like creating and embedding lexicons), tools for creating annotated corpora, accessing databases, comparing annotated data, or transforming linguistic information into vectors for use with various machine learning algorithms.
OpenIsis provides a library and tools to access CDS/ISIS databases, which are mostly used for bibliographic data (ISO2709, Z39.50) but also well suited for other catalogues due to the very flexible indexing mechanism. Based on a C library, there are also bindings for Perl and Java (Tcl to come).