The Kleene tokenizer, parser and abstract-syntax-tree (AST) builder are written in JavaCC, which is a parser generator that generates Java source code. Other modules, including the GUI (graphical user interface), the frame/symbol-table environment and the interpreter are written directly in Java. The interpreter is heavily dependent on OpenFst, a C++ library that it accesses via the JNI (Java Native Interface). The OpenFst library is also open-source and available under the Apache License, Version 2.
Kleene also depends on the Apache Commons, ICU, dom4j, and ROME libraries, which are also available under the Apache License, Version 2, or similar permissive licenses.
KRB: add info here about icons.