So, you like open source application. We also like it!
But, how many of us know that there are plenty of open source applications available for your daily requirements. You can save your time and energy just putting some efforts to find one which suites to your needs.
Alright, we are going to do this effort on your behalf. We are preparing a list of open source applications which you can try. Demo link of application will also be provided (where available) along with description, which we are taking from directly from application developers.

We hope our effort will save your time and energy.

We invite open source application developers and users (ofcourse! fans) to join this effort by putting your application details here!

So, here goes my favorite open source application!

QUOTE:

Joomla
Yes, this is my favorite CMS (Content Management Software). Joomla! is the best Content Management System and Web Application Framework as far as my liking.
From Joomla developers:

QUOTE:
Joomla! is one of the most powerful Open Source Content Management Systems on the planet. It is used all over the world for everything from simple websites to complex corporate applications. Joomla! is easy to install, simple to manage, and reliable.

Demo : http://demo.joomla.org/
Download : http://joomlacode.org/gf/project/joomla/frs/
More details : http://joomlacode.org/gf/project/joomla/frs/
Extensions : http://extensions.joomla.org/
Support Forum : http://forum.joomla.org/

Please continue this thread with post of your favorite application!

I like joomla too due to it's simplicity and support.
I also like phpNuke and posting details of the same below

PHP-Nuke is a news automated system specially designed to be used in Intranets and Internet. The Administrator has total control of his web site, registered users, and he will have in the hand a powerful assembly of tools to maintain an active and 100% interactive web site using databases.

PHP-Nuke runs well on the following Operating Systems:

* Linux
* Any Unix flavor
* OS/2
* Any Windows flavor
* MacOS
* FreeBSD

The system has been high tested on Linux systems, the other operating system has been reported by users that works great. In the future BeOS will be supported, this depends on the MySQL BeOS version to be released soon.

Homepage : http://phpnuke.org
Download page : http://phpnuke.org/modules.php?name=Downloads

Good effort!

Here is list of my favourite open source scripts.


1. phpBB - Discussion Forum Softwares
phpBB is a UBB-style dissussion board written in PHP backended by a MySQL database. It includes features such as posting/replying/editing messages, private messages, private forums, user and anonymous posting, robust theming, user ranking by posts or by special, admin definable, ranks, and much more.

Homepage: http://www.phpbb.com/
Demo site: http://www.phpbb.com/community/

2. phpMyFAQ - FAQ system
phpMyFAQ is a multilingual, completely database-driven FAQ system. It support various database systems and it also offers a content management system with a WYSIWYG editor, an image manager, flexible multi-user support, a news system, user tracking, language modules, templates, extensive XML support, PDF support, DocBook XML support, a backup system, and an easy to use installation script.

Homepage: http://www.phpmyfaq.de/
Demo site: http://www.phpmyfaq.de/referenzen.php

3. KnowledgeTree - Document management system
KnowledgeTree is a powerful Web-based document management system built on the popular LAMP (Apache/MySQL/PHP) stack. It is a leading PHP-based commercial document management software project. KnowledgeTree is used by Fortune 500 companies, community organizations, local and state governments, and educational and scientific institutions around the world.

Homepage: http://www.knowledgetree.com/
Demo site: http://demo.knowledgetree.com/

4. phpGroupWare - Software suite
phpGroupWare (formerly known as webdistro) is a multi-user groupware suite written in PHP. Its provides a Web-based calendar, todo-list, addressbook, email, news headlines, and a file manager. The calendar supports repeating events. The email system supports inline graphics and file attachments. The system as a whole supports user preferences, themes, user permissions, multi-language support, an advanced API, and user groups.

Homepage: http://www.phpgroupware.org/
Mirror site: http://downloads.phpgroupware.org/mirror
Demo site: http://phpgroupware.org/demos

5. eZ Publish - Content management system
eZ Publish is a content management system and development framework. As a content management system (CMS), its most notable feature is its revolutionary, fully customizable, and extendable content model. This is also what makes it suitable as a platform for general Web development. Its stand-alone libraries can be used for cross-platform, database independent PHP projects. eZ Publish is also well suited for news publishing, e-commerce (B2B and B2C), portals, and corporate Web sites, intranets, and extranets. eZ Publish is dual licenced between GPL and the eZ Publish professional licence.

Homepage: http://ez.no/developer/

Joomla and phpbb are excellent services for the newbie webmasters..to add to the list I'll suggest the blog platform..like Wordpress, MoveableType, TypePad and of course on board service mybb..there is also another one called YaBB forums..but I have not tried their service yet..

If you are looking for free, open source scripts, php scripts etc, this is the place where all the scripts are available:

http://freescripts.interviewhelper.org/

Thanks,
Nisha