GNU Emacs is a customizable text editor that is an interpreter and dialect with extension to support text editing with content-sensitive editing modes, built-in documentation, Unicode support, and more.
CVS is a version control system, an important component of Source Configuration Management (SCM). Using it, you can record the history of sources files, and documents. It fills a similar role to the free software RCS, PRCS, and Aegis packages.
Common Lisp is the standardized most powerful language with high-performance implementations in the world. It has lexical closures, multi-dispatch object system called CLOS, the metaobject protocol and macros.