Suggest me a good, free, open source, downloadable web application in php to make a good website for a organization or group having more than one member. Only administrator(s) can change the content of the website. Please do not suggest me any forum/blog applications like WordPress, phpBB etc.
Use one of the better-supported open-source CMSes for this reason.
I would suggest either Drupal or Joomla, both written in PHP. I am a strong Drupal fan, but Joomla has a lot of supporters as well.
Just some main bullet-points from the website of Drupal to show how versatile/powerful it is:
Collaborative Book - Our unique collaborative book feature lets you setup a "book" and then authorize other individuals to contribute content.detailed information
Friendly URLs - Drupal uses Apache's mod_rewrite to enable customizable URLs that are both user and search engine friendly.
Modules - The Drupal community has contributed many modules which provide functionality that extend Drupal core.detailed information
Online help - Like many Open Source projects, we can't say that our online help is perfect but have built a robust online help system built into the core help text. Available to you on your own site.detailed information
Open source - The source code of Drupal is freely available under the terms of the GNU General Public License 2 (GPL). Unlike proprietary blogging or content management systems, Drupal's feature set is fully available to extend or customize as needed.detailed information
Personalization - A robust personalization environment is at the core of Drupal. Both the content and the presentation can be individualized based on user-defined preferences.
Role based permission system - Drupal administrators don't have to tediously setup permissions for each user. Instead, they assign permissions to roles and then group like users into a role group.screenshot . detailed information
Searching - All content in Drupal is fully indexed and searchable at all times if you take advantage of the built in search module.
User authentication - Users can register and authenticate locally or using an external authentication source like Jabber, Blogger, LiveJournal or another Drupal website. For use on an intranet, Drupal can integrate with an LDAP server.detailed information
Polls - Drupal comes with a poll module which enables admins and/or users to create polls and show them on various pages.detailed information
Templating - Drupal's theme system separates content from presentation allowing you to control the look and feel of your Drupal site. Templates are created from standard HTML and PHP coding meaning that you don't have to learn a proprietary templating language.detailed information
Threaded comments - Drupal provides a powerful threaded comment model for enabling discussion on published content. Comments are hierarchical as in a newsgroup or forum.detailed information
Version control - Drupal's version control system tracks the details of content updates including who changed it, what was changed, the date and time of changes made to your content and more. Version control features provide an option to keep a comment log and enables you to roll-back content to an earlier version.screenshot
Blogger API support - The Blogger API allows your Drupal site to be updated by many different tools. This includes non-web browser based tools that provide a richer editing environment.detailed information
Content syndication - Drupal exports your site's content in RDF/RSS format for others to gather. This lets anyone with a News Aggregator browse your Drupal sites feeds.detailed information
News aggregator - Drupal has a powerful built-in News Aggregator for reading and blogging news from other sites. The News Aggregator caches articles to your MySQL database and its caching time is user configurable.detailed information
Permalinks - All content created in Drupal has a permanent link or "perma link" associated with it so people can link to it freely without fear of broken links.
Apache or IIS, Unix / Linux / BSD / Solaris / Windows / Mac OS X support - Drupal was designed from the start to be multi-platform. Not only can you use it with either Apache or Microsoft IIS but we also have Drupal running on Linux, BSD, Solaris, Windows, and Mac OS X platforms.detailed information
Database independence - While many of our users run Drupal with MySQL, we knew that MySQL wasn't the solution for everyone. Drupal is built on top of a database abstraction layer that enables you to use Drupal with MySQL and PostgreSQL. Other SQL databases can be supported by writing a supporting database backend containing fourteen functions and creating a matching SQL database scheme.detailed information
Multi-language - Drupal is designed to meet the requirements of an international audience and provides a full framework to create a multi-lingual website, blog, content management system or community application. All text can be translated using a graphical user interface, by importing existing translations, or by integrating with other translation tools such as the GNU gettext.detailed information
Administration and analysis
Analysis, Tracking and Statistics - Drupal can print browser-based reports with information about referrals, content popularity and how visitors navigate your site.screenshot . detailed information
Logging and Reporting - All important activities and system events are captured in an event log to be reviewed by an administrator at a later time.screenshot . detailed information
Web based administration - Drupal can be administered entirely using a web browser, making it possible to access it from around the world and requires no additional software to be installed on your computer.screenshot
Discussion forums - Full discussion forum features are built into Drupal to create lively, dynamic community sites.detailed information
Performance and scalability
Caching - The caching mechanism eliminates database queries increasing performance and reducing the server's load. Caching be tuned in real time and many high-traffic sites have performed very well under load.detailed information