Speedo

Speedo is an open source implementation of the JDO (TM) 1.0.1 specification. It is hosted by OW2.

Speedo main benefits

Possible choice of optimistic or pessimistic transaction mode
Locking managed by Speedo itself or by the database (clustering support)
Cache of persistent objects (L2), with a choice of several replacement policies (LRU | MRU | FIFO | ...) configurable per class.
Data prefetching at query evaluation time: later accesses to objects will not require any I/O to the data store
Lazy loading of data and support of fetch groups (JDO2)
Management of relation ships (coherency management)
Able to create the SQL schema dynamicaly and to provide sql script
Various identifier support (application (composite or single), SQL sequence, speedo)
Lot of types supported
Lot of databases supported (Oracle, MS SQL server, Mysql, Postgres, ...)
Through JORM and MEDOR, access to legacy relational databases, as well as any other data store supported by JORM and MEDOR
Http console for administration
Soon fully JDO 2.0 ...

Speedo reuses several OW2 frameworks:

JORM, a framework for mapping objects onto persistent supports such as relational databases.
MEDOR, a query framework permitting queries over distributed data sources.
Perseus is a persistence framework managing several aspects such as caching, pooling, and concurrency control.
Fractal, the OW2 component model used to build middleware components and frameworks.
Julia, Fractal's reference implementation.
ASM, a framework to manage Java byte code.
Monolog, an API of logging which aims at being independant from the logging system (log4j, jdk1.4).