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.
Expresso is an interpreter for the programming language Expresso. The interpreter can be included within a Java applet or application. This distribution contains a Java applet which demonstrates its use.
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.