Date: 05/19/07 (Java Web)    Keywords: database, sql, java

HSQLD is a mature, high-performant database written in Java. It is used in several high profile popular commercial and open source products like Open Office 2.0 (Office productivity suite; competitor of MS Office), JBoss (Application Server), JFox (Application Server), Jonas (Application Server), Mathemetica, Hibernate (ORM), Jira (Defect Tracking), TrackStudio (Defect Tracking), C-JDBC (Database Clustering) etc. [...]

Source: http://blog.taragana.com/index.php/archive/the-case-for-hsqldb-as-rdbms-for-java-development/