 <p>Both <a href="http://www.h2database.com" rel="nofollow">H2</a> and <a href="http://hsqldb.org/" rel="nofollow">HyperSQL</a> support embedded mode (running inside your JVM instead of in a separate server) and saving to local file(s); these are still SQL databases, but with Hibernate there's not many other options.</p>