mu is a collection of utilities for maildirs, in particular for indexing and searching them. mu fills a database with information about your emails, which can then be queried using an easy query language. It can work stand-alone or be integrated with a mail client. It also provides an emacs-based email client ("mu4e") and bindings for Guile/Scheme.
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.
The Autotoolset package complements the GNU build system by providing automatic generation of legal notices, automatic generation of GNITS-standard directory trees, a rudimentary portability framework for C++ programs, support for writing portable software that uses both Fortran and C++, additional support for writing software documentation in Texinfo and LaTeX, and a manual introducing both Autotools and the GNU build system in a unified task-oriented manner.
Argh! is an esoteric programming language in the spirit of Befunge, Brainfuck, and friends. It is a nice and simple language with two dimensional code-flow, a combined code/data array, an infinite stack, regular characters for all instructions, no strange braces or symbols, no unnecessary arithmetic operators (add and sub are all you need), and countless other features it doesn't have. The distribution includes interpreters for Argh! and Aargh! (an extended Argh! that is most likely Turing complete), the official specification, editing modes for emacs and vim, and lots of examples.
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.
GNU Libidn is an implementation of the Stringprep, Punycode, and IDNA specifications defined by the IETF Internationalized Domain Names (IDN) working group. It is used to prepare internationalized strings (such as domain name labels, usernames, and passwords) in order to increase the likelihood that string input and string comparison work in ways that make sense for typical users throughout the world. The library contains a generic Stringprep implementation that does Unicode 3.2 NFKC normalization, mapping and prohibition of characters, and bidirectional character handling. Profiles for iSCSI, Kerberos 5, Nameprep, SASL, and XMPP are included. Punycode and ASCII Compatible Encoding (ACE) via IDNA are supported.