<a href='http://www.objectdb.com'>ObjectDB for Java/JDO</a> is a powerful yet compact Object Database (ODBMS) for Java, written entirely in Java, and compliant with the Java Data Objects (JDO) standard developed by Sun. ObjectDB for Java/JDO is designed to efficiently handle databases of various sizes, ranged from a few KBs to hundreds of GBs. Among its <a href='http://www.objectdb.com/database/jdo/java-features/'>features</a> are small footprint, high performance, rapid development, easy deployment and flexible architecture (1-Tier, 2-Tier or N-Tier). A <a href='http://www.objectdb.com/database/jdo/free-download/'>Free Download</a> is available for non commercial use.