Here is a non-exhaustive (73 so far) list of some Free Software projects which we contributed [1] to:
See also our BeezNest's Free Software Specialities.
      - apt-proxy
 - Asterisk
 - Auto Nice Daemon (AND)
 - AWstats
 - Bacula
 - BNPanel
 - Cedar Backup
 - Chamilo
 - Claroline
 - COnfigurator for GNOME (COG)
 - Crystal Space
 - DCL
 - Debian / Debian Education / Debian-Edu
 - Debian-Installer
 - Dokeos
 - Dolibarr
 - dotProject
 - Drupal [1][2][3][4]
 - Etherboot
 - Evolution
 - Evolution mail template plugin
 - EXACT (POP- and IMAP-before-SMTP daemon)
 - FreeCiv
 - FreeNAS
 - FreeRADIUS
 - Fwanalog
 - Galeon
 - Glasnost
 - GNOME
 - Gnoppix
 - InitNG
 - IPblocker
 - ISPConfig
 - JFFNMS
 - Knoppix
 - LAM
 - Librassoc
 - LibSSH extension for PHP
 - LTSP
 - MnoGoSearch
 - Netatalk
 - Netsaint/Nagios
 - Ntop
 - NVU
 - OpenOffice.org
 - Open ERP
 - OpenC2C
 - p910nd
 - Pancho Project
 - Pessulus
 - PhpCompta
 - PHPiCalendar
 - phpLangEditor (Firefox extension)
 - PhpLdapAdmin
 - PHP-PENS
 - Plume
 - PostgreSQL
 - qemu
 - Replicator
 - SER
 - Sip Express Router (SER)
 - Swocket
 - THT
 - TORCS
 - Tulip (Editor written in PHP-GTK)
 - Ubuntu
 - UmiGumi / DLS
 - Webalizer
 - Webcalendar
 - Widelands
 - XAMS
 - Zebra / Quagga
 - Xapian
 - ...
 
See also our BeezNest's Free Software Specialities.
[1] code, documentation or suggestions which have been applied
This article was first written in January 2006 for the BeezNest technical website (http://glasnost.beeznest.org/articles/324).