Redstone Prevalent Storage is minimalistic prevalent storage for Java SE 5.0 that replaces the need for JDBC and an RDBMS for small and mid-sized applications. The library is comprised of an intentionally small set of concise interfaces and classes, and can be suitable for many types of applications where the data storage does not necessarily require an RDBMS. The library is heavily influenced by Prevayler and the Prevayler team (who should receive all credit).
Native XmlDB Query Daemon is a client-server version of the Sleepycat native XML database deployed as an Apache module. The client is a pure Java API, supporting XQuery, XPath, and an Xml:DB API layer. It comes with a graphical admin console. Server binaries are provided for Linux x86 and x86-AMD64; for other platforms, compile from source.
phpDatabase.net is a pure PHP database script which can be used for an application as a light-weight database. It implements basic database functions like creating and dropping database; creating, changing, and dropping tables and sequences; selecting, inserting, updating, and deleting data from tables; automatic locking of files, so simultanous changing the data is possible; transaction processing, commiting, or rolling back of changes; and a default auto-commiting mode. It is packaged as a single PHP script.
databeans is a fully object oriented (not relational) persistence framework for Java, based on the use of the JavaBeans accessor methods to read and write data on disk instead of in the classes' instance fields. It is distributed (through RMI), transactional (with the 4 ANSI isolation levels supported), garbage collected (backed by an on-disk heap called "heapspace"), and has persistent versions of the Collection classes. It aims to provide a full-fledged solution for enterprise application development.
Data stream processing toolkit (dspt) is intended for processing huge amounts (gigabytes) of data in an efficient manner. The structure of the data files is user-defined, and the queries are written in a declarative style. Currently included algorithms range from simple filtering on predicates to aggregation and sorting. It also includes some convenience classes (e.g. for accessing BerkeleyDB databases). The toolkit does not offer as wide a range of operations as an RDBMS, but some measurements of simpler queries have shown it to be more than 10x faster than PostgreSQL.