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.
Xtla is the Emacs front-end to the GNU Arch revision control system. It provides user-friendly wrappers for tla native commands and some higher level features such as the bookmark manager. The main features are a PCL-CVS-like interface for tla inventory and tla changes, an archive browser, good integration in Emacs, a bookmark manager, integration with ediff, Emacs's graphical diff tool, an interface to view missing patches from all your partners with a single command, and an Emacs mode for arch-related files (log files, =tagging- method).
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.
Darius Tools is a collection of miscellaneous scripts which are useful for a variety of purposes. They are all designed to be faster and easier to use than the command line that would normally be required to accomplish the same task. For example, there are scripts for mass conversion of WAV files to Ogg files and Ogg files to WAV files, for converting LaTeX to PostScript and viewing the output in ggv, for creating image thumbnails, for converting from the Euro to another currency, for automated updating via FTP and for removing backups recursively. The Darius Tools are split among several packages according to different categories.