Advantage in using an open source software is:-

1. As it is open source, so the source files can be edited and can be modified as per your needs. Thus it can cater to needs of any individual or corporation.

2. Most of them are free so even if you are not satisfied you are not at a loss. Though in most cases you will come out satisfied.

3. You have a vast community and also volunteers who are ready to help you create your site or troubleshoot if you get into any kind of issues.

4. It is regularly updated as other commercial softwares so you will remain updated as and when technology changes.

5. Another advantage is you can manage your site very easily as the backend is so designed that any layman can change the look and content easily.

6. You will also find many addons or extensions for each softwares which adds feather to the cap.

There are various Open source softwares in the market out of which I have listed a few and important ones. These are

1. Wordpress- Wordpress last year achieved first price in open source softwares or the best CMS award. Wordpress is really easy to install, configure and maintain. It has advantage of having lots of beautiful templates for free. At the backend you can select and install the templates.

  It has many plugins which helps in creating different types of website. For a layman wordpress seems to be more easy than other scripts.

  Wordpress has Plugins or extensions and Widgets that can be placed on various positions which differs based on the templates. Jump to Wordpress.

2. Joomla- It is more user friendly than any of its competitor. It is now a most enviable script. It can also be modified to suit your needs. It’s not that complex to maintain the site. After release of Joomla 1.7 it has got many distinct advantages over its rivals. Membership component which was missing in Joomla 1.5 is now added in Joomla 1.7.

  Different rules and permissions can be created as in drupal to manage your user database. Thousands of free templates are available in the market which can be downloaded and used in your sites.

  Joomla has a big community of volunteers, always ready to help its users. So it is marching way ahead of others.

"Plugins in wordpress" corresponds to "Components in Joomla". And "wordpress widgets" are like "modules in Joomla". Dive into Joomla.

3. Drupal- This is for the genius as with this you can create any website of any complexity. Sky is the limit. This has two main hands - left hand is "CCK" and right hand is "VIEWS". CCK is Content Construction Kit where you can create any type of content, and VIEWS is used to display the content created in many different ways.

Drupal also has a vast community and many top class organisations use drupal to create their site.

"Joomla Components" corresponds to "Drupal Modules" and "Joomla Modules" corresponds to "Drupal Blocks". Explore Drupal.

So same name has different terminology in different Scripts.

Overall idea of being open source is to cater to a large mass rather than confined to big shots who can pay more money.

With this anyone can create their own website very easily and have a presense online.

There are various other open source softwares which are available in the market but these three are the leaders.