DDMSence (pronounced "dee-dee-em-Essence") is a Java API which supports the DoD Discovery Metadata Specification (DDMS).
Egg is an interpreter for an anonymous language that is described in Dijkstra's book "A Discipline of Computer Programming". It is written in Java using the SableCC package.
OpenJX is a Java XML form language. It is meant to be like Adobe's Flex language, but it uses Java at its core.
PS3I is another Scheme interpreter, nearly R4RS compliant, written in Java. PS3I is a concurrent, multi-threaded, multi-user interpreter that may be used from a command line or via servlets.