An attempt to embed LaTeX environments such as display math or figures into the source buffers. Provides the manual, mailing list, screenshots and download.
A package that provides distinct support for doing labels, references and citations in LaTeX for both Emacs and XEmacs. It runs as a minor mode with any LaTeX major mode, most notably AUCTeX. Bundled and preinstalled with Emacs since version 20.2, or ...
GNU's Ubiquitous Intelligent Language for Extension, a library implementation of the Scheme language plus various convenient facilities. Designed to be linked into programs to make them extensible.
Object-oriented extension to Guile; very close in spirit to Common Lisp Object System, CLOS (CLtL2), but adapted for Scheme language; gives full OO system with multiple inheritance, generic functions with multi-method dispatch.
Powerful (Turing-equivalent) implementation of traditional Unix macro-expansion program, designed as preprocessor to more stubborn languages. Ugly, but fairly standard, available on most platforms.