Jx/J&, languages for extensible, composable software frameworks
Nested inheritance is a language feature that provides scalable extensibility, the ability to extend a body of code while writing new code propotional to the differences in functionality and while ensuring type safety.
Polyglot, an extensible Java compiler framework
Polyglot is an extensible compiler framework that supports the easy creation of compilers for languages similar to Java, while avoiding code duplication. The Polyglot framework is useful for domain-specific languages, exploration of language design, and for simplified versions of Java for pedagogical use. Polyglot has been used to implement several modifications to Java, including Jif, JMatch, and Jx.