The Z Object Publishing Environment consists of an object database (ZODB) and application server (ZServer) written in Python.

ODMG 3.0 compliant DBMS (including OQL) with manipulatable classes, templates and triggers. Supports multi-database objects. C++ and Java bindings. [Free for educational purposes]

Links to evaluations, benchmarks and products.

ODBMS compliant with the ODMG 3.0 standard. It's available as Just Edition (for small applications) and Enterprise Edition with extra components for replication, load-balancing and fault-tolerance. Supports Windows and Linux. Free Just version availab...

An LGPL extension to the Zope DB that provides indexing and querying.

Internet accessible object-oriented database that allows inherently secure remote access to (legacy) data from fixed and wireless devices. Also provides on-line schema evolution and access audit mechanisms.

An object-based database management system optimized for user interaction instead of transaction processing. It includes a database browser providing secure access to its server across the Internet. C++ binding for several flavours of UNIX. [Source co...

A short comparison of ObjectStore, Versant, Poet, and Objectivity mostly focusing on the evaluation criteria.