Soholaunch is a software product that makes it easy for people of all experience levels to create and maintain a great website. It reins in the hard parts of building a website and presents them in a way that non-geek can understand and control.
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WordPress is a state-of-the-art semantic personal publishing platform with a focus on aesthetics, web standards, and usability. What a mouthful. WordPress is both free and priceless at the same time.
More simply, WordPress is what you use when you want to work with your blogging software, not fight it.

B2evolution is a free blog tool for the next generations of blogs. It includes all the features of traditional blog tools, and extends them with evolved features such as file & photo management, advanced skinning, multiple blogs support as well as detailed user permissions.... not to mention third party plug-ins! 

Geeklog is another a cross between a blog and CMS (Content Management System) that can be set up in just minutes.

Drupal is a full CMS (Content Management System) equipped with a powerful blend of features that can support a variety of websites randing form personal weblogs to large community-driven websites.

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!  simple to manage, and reliable. 

Mambo is a content management system (CMS) for creating and managing websites through a simple web interface. It has attracted many users due to its ease of use. Mambo also includes more advanced features such as page caching to improve performance on busy sites, advanced templating techniques, and a fairly robust API. It can also automate many tasks such as web indexing for static pages. Mambo can provide RSS feeds, printable versions of pages, news flashes, blogs, forums, polls, calendars, website searching, language internationalization, and other possibilities.

Nucleus CMS is an open-source blog management software package written in PHP, with a MySQL backend,  It is used to manage frequently-updated Web content. With a little tweaking (mainly to skins) it might be considered a light content management system, although there is no facility to upload file types other than graphic files to be displayed within the blog pages.

ocPortal is website software which drives dynamic and interactive sites; use the quick installer to install ocPortal in minutes, and then after running the simple setup wizard you have a powerful website ready for use! By providing a wide-range of flexible general-purpose features for you to mix as you need, ocPortal enables you to build a highly personalized site (not just another cloned blog, forum, or portal) for far far less than you'd pay a web design company. 

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.

PostNuke is software that creates an impressive, dynamic web site and provides the webmaster with a site they can administer with a minimal amount of HTML knowledge through a web browser.

XOOPS is a program that allows administrators to easily create dynamic websites with great content and many outstanding features. It is an ideal tool for developing small to large dynamic community websites, intra company portals, corporate portals, weblogs and much more.

Openads 2.0 is an ad server written in PHP that allows you to place banners on your website and lets you manage your banners in a professional way. Openads is open-source which means you have access to the source code, licensed under the General Public License.

osCommerce is an Open Source based online shop e-commerce solution that is available for free under the GNU General Public License. It features a rich set of out-of-the-box online shopping cart functionality that allows store owners to setup, run, and maintain their online stores with minimum effort and with no costs, fees, or limitations involved.

Zen Cart™ truly is the art of e-commerce; a free, user-friendly, open source shopping cart system. The software is being developed by group of like-minded shop owners, programmers, designers, and consultants that think e-commerce could be and should be done differently.

PhpBB Since its creation in 2000, phpBB has become the most widely used Open Source forum solution. Like its predecessors, phpBB 3.0 “Olympus” has an easy to use administration panel and a user friendly installation process, which allows you to have a forum set up in minutes.

Simple Machines Forum — SMF in short — is a free, professional grade software package that allows you to set up your own online community within minutes. Its powerful custom made template engine puts you in full control of the lay-out of your message board and with our unique SSI — or Server Side Includes — function you can let your forum and your website interact with each other. SMF is written in the popular language PHP and uses a MySQL database. It is designed to provide you with all the features you need from a bulletin board while having an absolute minimal impact on the resources of the server.

Crafty Syntax Live Help is an open source live support solution that helps customer support. Crafty Syntax includes a large range of features to allow multiple operators, multiple departments and multiple languages to be used. Crafty Syntax Live Help is free and is programmed in PHP with MySQL for the database. Other highlighted features include the ability to create your own questions, auto inviting visitors, referrer tracking, page tracking, ability to view what the customer is typing as they type, multiple chat sessions, sound alert, leave a message if offline, push urls, quick responses, Customizable graphics, and multiple operators.

MediaWiki is an extremely powerful, scalable software and a feature-rich wiki implementation, that uses PHP to process and display data stored in its MySQL database.
Pages use MediaWiki's wikitext format, so that users without knowledge of XHTML or CSS can edit them easily.
When a user submits an edit to a page, MediaWiki writes it to the database, but without deleting the previous versions of the page, thus allowing easy reverts in case of vandalism or spamming. MediaWiki can manage image and multimedia files, too, which are stored in the file system. For large wikis with lots of users, MediaWiki supports caching and can be easily coupled with Squid proxy server software.

phplist is a one-way email announcement delivery system. It is great for newsletters, publicity lists, notifications, and many other uses. # The Web Interface lets you write and send messages, and manage phplist over the internet.
phplist keeps sending messages from your web server, even after you shut down your computer.
100 000 + subscribers. phplist is designed to manage mailing lists with hundreds of thousands of subscribers. phplist is excellent with smaller lists too!

phpMyFAQ 2 is a multilingual, completely database-driven FAQ-system. phpMyFAQ also offers a multi-language Content Management-System with a WYSIWYG editor and an Image Manager, flexible multi-user support with user and group based permissions on categories and records, a wiki-like revision feature, a news system, user-tracking, language modules, enhanced automatic content negotiation, templates, extensive XML-support, PDF-support, a backup-system, a dynamic sitemap, related articles, tagging, RSS feeds, built-in spam protection systems, and LDAP support.

Coppermine is a multi-purpose fully-featured and integrated web picture gallery script written in PHP using GD or ImageMagick as image library with a MySQL backend.

Gallery, the open source web based photo album organizer. Gallery gives you an intuitive way to blend photo management seamlessly into your own website whether you're running a small personal site or a large community site.

DotProject is a Project Management tool. Check out the official web site where you will find a Live Demo.

eGroupWare is a free enterprise ready groupware software for your network. It enables you to manage contacts, appointments, todos and many more for your whole business.
eGroupWare is a groupware server. It comes with a native web-interface which allowes to access your data from any platform all over the planet. Moreover you also have the choice to access the eGroupWare server with your favorite groupware client (Kontact, Evolution, Outlook) and also with your mobile or PDA via SyncML.

WebCalendar is a PHP-based calendar application that can be configured as a single-user calendar, a multi-user calendar for groups of users, or as an event calendar viewable by visitors.

WebCalendar can be setup in a variety of ways, such as...

• A schedule management system for a single person
• A schedule management system for a group of people, allowing one or more assistants to manage the calendar of another user
• An events schedule that anyone can view, allowing visitors to submit new events
• A calendar server that can be viewed with iCalendar-compliant calendar applications like Mozilla Sunbird, Apple iCal or GNOME Evolution or RSS-enabled applications like Firefox, Thunderbird, RSSOwl, FeedDemon, or BlogExpress.