DataNucleus AccessPlatform is a standards-compliant Java persistence product. It is fully compliant with the JDO1, JDO2, JDO2.1, JDO2.2, JDO3, JPA1, JPA2 and JPA2.1 Java standards, and provides a REST API. It complies with the OGC Simple Feature Spec for persistence of geospatial Java types. It allows access to all popular RDBMS available today, together with the MongoDB, LDAP, NeoDatis, JSON, Excel/ODF spreadsheets, XML, BigTable, HBase, and Neo4j databases.
Butterfly Persistence is a simple, no nonsense Java persistence API. It aims to provide a simple relational persistence API. Its features include automatic/manual connection management, easier JDBC operations via JDBC templates (Spring style), simple object relational mapping, and map reading for dynamic queries. It provides a simple and pragmatic approach to persistence and will either help you, or get out of the way and let you do the job manually.
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).
The Generic Repository (grepo) is a framework for Java which allows you to access (database) repositories in a generic and consistent manner. Using grepo, it is generally no longer required to provide all the boilerplate code which is necessary in order to access (database) repositories from Java. All you have to do is write appropriate database code (queries, procedures, functions, etc.), an appropriately annotated Java interface, and very little Spring configuration.
Objectify-Appengine is a thin Java wrapper around Google App Engine's low-level datastore API that allows you to persist type-safe POJO objects. It provides a human-friendly query interface, generified key, query, and prepared query classes, GWT-able entity objects, and transactions in one lightweight jar file with no dependencies.
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).