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).
Tephlon is an easy PHP persistence library. It has a highly modular OOP design and a no-SQL storage system. It stores any object or variable safely and tidily on disk for fast access. The API is meant to be easy and fast to learn. It features Java-style key-value maps, namespaces, easy Codeigniter integration, programmable lifetime of records, a multi-driver architecture, reliable and well-tested code, and easy incremental backup of data with SVN or GIT.
persistence4j is a small and lightweight Java object persister that uses JDBC to persist data into a relational database. The library frees you from writing the Data transfer objects - just create a POJO and simply save it. Transactional and non-transactional connections are supported and can be configured from the simple properties file.
minidb is a Python module that utilizes the SQLite3 database library in order to store and retrieve Python objects. It utilizes Python's __slots__ mechanism to determine the column names, and uses the class name for table names. Data is always stored as text in the database, but will be converted using the type specified in __slots__ (which therefore has to be a dict).
KiokuDB is a frontend to various data stores. Its purpose is to provide persistence for "regular" objects with as little effort as possible, without sacrificing control over how persistence is actually done, especially for objects that are harder to serialize. KiokuDB is also non-invasive: it does not use ties, AUTOLOAD, proxy objects, sv_magic, or any other type of trickery. Many features important for proper Perl space semantics are supported, including shared data, circular structures, weak references, tied structures, etc.