Disk Information Utility

https://diskinfo-di.sourceforge.io/

Diagram creation program, similar to Visio

https://live.gnome.org/Dia

Console Interface to configure ports

https://bitbucket.org/m1cro/d4p/

Simple english/german dictionary

http://www.de.freebsd.org/~wosch/dict/dict.cgi

Dict protocol (RFC 2229) server

http://www.dict.org/

GNU diff utilities

http://www.gnu.org/software/diffutils/diffutils.html

Monospace bitmap font, primarily aimed at programmers

http://www.donationcoder.com/Software/Jibz/Dina/

Open source video codec from the BBC

http://dirac.sourceforge.net/

Graphical diff tool

http://freecode.com/projects/dirdiff/

Client for managing and downloading certificate revocation lists

http://www.gnupg.org/aegypten2

Frontend to xgamma

http://gnu.ethz.ch/linuks.mine.nu/displaycalibrator/

Distribute compilation of C(++) code acrosss machines on a network

http://distcc.org

Extremely fast library for floating-point convolution

http://cr.yp.to/djbfft.html

DjVu base libraries and utilities

http://djvu.sourceforge.net/

FTP benchmark program

http://www.kegel.com/dkftpbench/

Another hyper make utility

http://code.google.com/a/apache-extras.org/p/dmake/

Portable debug memory allocation library

http://dmalloc.com/

X11 menu application designed for the dwm window manager

https://tools.suckless.org/dmenu

Tool for dumping DMI (SMBIOS) contents in human-readable format

https://www.nongnu.org/dmidecode/

Distributed.net distributed computing project client

http://www.distributed.net/

Simple sudo alternative to run commands as another user

https://github.com/slicer69/doas/

Meta-port for the different versions of the DocBook DTD

http://www.oasis-open.org/docbook/

DocBook SGML DTD

http://www.oasis-open.org/docbook/

DocBook SGML DTD into nroff/troff -man macros converter

https://www.oasis-open.org/docbook/tools/dtm/

Generates various output formats from DocBook SGML documents

http://sources.redhat.com/docbook-tools/

DocBook XML DTD

https://www.oasis-open.org/docbook/

DocBook W3C XML Schema

https://www.oasis-open.org/docbook/xmlschema/1.0b1/

XSL DocBook stylesheets

http://docbook.sourceforge.net/projects/xsl/

Emacs lisp modules for editing DocBook documents

http://nwalsh.com/emacs/docbookide/

Docker containment system

https://github.com/kvasdopil/docker

DOCSIS(tm) binary configuration file encoder/decoder

https://github.com/rlaager/docsis

Doom data files (Doom, Doom II, Hexen, Heretic and Strife)

Complete Doom-based game IWAD that is Free Software

http://freedoom.sf.net/

Improved and extended version of Doom

http://doomlegacy.sourceforge.net/

Emulator of a PC with DOS

http://dosbox.sourceforge.net/

Simple, powerful configuration-file parser

https://github.com/williamh/dotconf

Doulos SIL TrueType font collection

http://scripts.sil.org/cms/scripts/page.php?item_id=DoulosSILfont

Doulos SIL TrueType font collection, compact variant

http://scripts.sil.org/cms/scripts/page.php?item_id=DoulosSILfont

Secure, fast and powerful IMAP and POP3 server

https://www.dovecot.org/

Documentation system for C, C++, and other languages

https://www.doxygen.org/

The Droid typeface family

https://www.droidfonts.com/

Database driven web content management system (CMS)

https://www.drupal.org/

Database driven web content management system (CMS)

https://www.drupal.org/

DSSSL stylesheets for the DocBook DTD by Norman Walsh

http://sourceforge.net/projects/docbook/

Spawns dhclients for a dual-stack network

English to Thai dictionary for GNUstep

http://www.eskimo.com/~pburns/Dictionaries/

Duo unix integration package

http://duosecurity.com

Backup tool that uses librsync and GnuPG

http://duplicity.nongnu.org

Shell front end for the duplicity backup tool

http://duply.net

DVD burning software

http://fy.chalmers.se/~appro/linux/DVD+RW/