GNU TeXmacs is a free wysiwyw (what you see is what you want) editing platform with special features for scientists. The software aims to provide a unified and user friendly framework for editing structured documents with different types of content: text, mathematics, graphics, interactive content. TeXmacs can also be used as an interface to many external systems for computer algebra, numerical analysis, and statistics. New presentation styles can be written by the user and new features can be added to the editor using Scheme.
Geiser is a generic Emacs/Scheme interaction mode, featuring an enhanced REPL and a set of minor modes that improve Emacs' basic major mode for Scheme. The main features provided are evaluation of forms in the namespace of the current module, macro expansion, loading of files and modules, namespace-aware identifier completion, automatic documentation, jumping to the definition of an identifier, access to documentation, listings of identifiers exported by a given module, and rudimentary support for debugging. Geiser supports Guile and Racket.
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.
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.
SLIME is an integrated development environment for Common LISP which does everything you would expect from an IDE: code evaluation, compilation, macro expansion, and auto-completion. It also finds definitions of functions, and marks LISP forms which the compiler finds to be erroneous. It provides easy access to implementation-specific online documentation as well as the ability to look up symbols in the ANSI Common Lisp HyperSpec. Further, it includes an interactive debugger and object inspector.