XEmacs (formerly known as Lucid Emacs) is a powerful, extensible text editor with full GUI support, initially based on an early version of GNU Emacs 19 from the Free Software Foundation and since kept up to ate with recent versions of that product. XEmacs stems from a collaboration of Lucid, Inc. with Sun Microsystems, Inc. and the University of Illinois with additional support having been provided by Amdahl Corporation, INS Engineering Corporation, and a huge amount of volunteer effort.
CSDE (CSharp Development Environment for X/Emacs) is a full-featured mode for CSharp development in Emacs/XEmacs. Features include font-lock, indentation rules, grammatical parsing, auto complete, automatic documentation of classes, documentation checking of classes, namespace generation, using sorting, and much more. This is a conversion of the JDE for Emacs / XEmacs to CSharp.
ECB is a source code browser for (x)emacs. It displays a couple of windows that can be used to browse directories, files, and file contents like methods and variables. It supports source code parsing for languages like Java, C, C++, Elisp, Scheme, Perl, TeX, LaTeX, etc. In addition, it offers an (optional) permanent "compile window" at the bottom of the emacs frame, which is used to display all help and compile output. The rest of the frame is called the "edit area", which can be divided into several edit windows that are used for editing the sources. Deleting some of the edit windows neither destroys the compile window nor the browsing windows. It requires the CEDET suite.
Aquamacs is a Mac-like version of the powerful Emacs text editor that runs as a standard OS X application. It features extensive customization that enables it to conform better with Apple's standard Human Interface Guidelines (HIG) than standard versions of the editor do. It provides a more Mac-like user experience than Carbon Emacs.
Pymacs is a powerful tool which, once started from Emacs, allows both-way communication between Emacs Lisp and Python. Pymacs in intended for using Python as an extension language for Emacs rather than the other way around, and this asymmetry is reflected in some design choices. Within Emacs Lisp code, one may load and use Python modules. Python functions may themselves use Emacs services and handle Emacs Lisp objects kept in Emacs Lisp space.