Drupal

Preferred license: GNU General Public License (GPL)
Drupal is a web content management system and web application framework. It is also a vibrant, growing, and fun community of programmers, activists and communicators. The core Drupal software is the poster child for Web 2.0, community driven web site software. The highly extensible architecture supports well over a thousand sub-projects in the form of contributed modules and themes.
 
Current Projects
by Gábor Hojtsy, mentored by Gerhard Killesreiter
by Andrew Morton, mentored by Angela Byron
by Jakob Petsovits, mentored by Andy Kirkham
by Klaas Van Waesberghe, mentored by Theodore Serbinski
by Matthias Hutterer, mentored by Nicholas Thompson
by Anthony Oliver, mentored by Jeff Eaton
by Amila Sampath, mentored by Theodore Serbinski
by Balazs Dianiska, mentored by Simon Hobbs
by Scott Hadfield, mentored by Khalid Baheyeldin
by Jakob Perz, mentored by Gordon Heydon
by Blake Joseph Lucchesi, mentored by Robert T. Douglass
by Christopher P. Bradford, mentored by Károly Négyesi
by Kyle Cunningham, mentored by Darrel O'Pry
by Allister Beharry, mentored by Rok Žlender
by William L. White, mentored by Ian Ward
by Gartheeban Ganeshapillai, mentored by Kaustubh Srikanth