With MetaModel, you use a type-safe SQL-like API for querying any datastore. It is a data access framework providing a common interface for exploration and querying of different types of datastores. It isn't a data mapping framework. Instead, it emphasizes abstraction of metadata and the ability to add data sources at runtime, making MetaModel great for generic data processing applications, but less so for applications modeled around a particular domain.
BitNami MAPPStack is an easy-to-install, ready-to-run binary distribution of Apache, PostgreSQL, and PHP, including the phpPgAdmin tool. It runs in Mac OS X and allows you to quickly setup a development or production Web application environment. BitNami Stacks are easy to install, independent, integrated, and relocatable.
Apache Jackrabbit is a fully conforming implementation of the Content Repository for Java Technology API (JCR). A content repository is a hierarchical content store with support for structured and unstructured content, full text searching, versioning, transactions, observation, and more. Typical applications that use content repositories include content management, document management, and records management systems.
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.
Spinneret is a structured storage engine that can be thought of as an extended tuple storage system. It takes the best aspects of relational, object, and hierarchical databases and throws away the dead weight associated with those technologies. The benefit of Spinneret is that its data model is incredibly flexible, allowing it to expose its underlying data in any number of ways. It operates similar to an object database, but without hard ties to an originating language, and can also behave like a relational database without the burden of complex joins.
Rasqal is a C library for querying RDF graphs, supporting the SPARQL, RDQL, and LAQRS languages. It provides APIs for creating a query and parsing query syntax. It features pluggable triple-stores and matching interfaces, query engines for executing the queries, an API for manipulating results as bindings, and multiple ways to format the results to XML, CSV, TSV, and JSON. It uses the Raptor RDF parser to return triples from RDF content, and can alternatively work with the Redland RDF library's persistent triple stores. It is portable across many POSIX systems.