H2 is an embeddable RDBMS written in Java
Free database schema discovery and comprehension tool
A powerful, cross platform, SQL database system
Java persistence using JDO, JPA or REST
UBA Probenverwaltungssystem (Specimen Management System)
Java Editor For DataTables
TPC-C Like workload generator
Spatial extension for relational database system. Follows OGC standars
although fully functional, this is a pre-framework that you can extend