Magento is an open source online shopping store builder developed by a consortium of developers from all over the world, they offer both a free edition that delivers the performance and features required to build a great online store, and Magento Commerce that is designed for large businesses and corporations that require online technical support with installation, usage and configuration and for this service they charge a fee.
Developers of Magento can implement the core files and extend its functionality by adding new plug ins and modules provided by other developers from around the world, so the development of the product is always ongoing and advancing. Since the first public version was released way back in 2007, Magento has been developed and customized in order to provide a basic eCommerce platform for selling a great variety of products online.
An ever increasing range of templates and Magento themes can be purchased from various developers and designers from all around the world, so you can always change the appearance and look of your online ecommerce store, there is also a range of extensions to allow shopping feeds to simplify the setting up of your online store, Magento like Joomla is a content management system and as such works in a similar fashion.
When your goal is to build an online Ecommerce website there are other choices and options out there for store building, not only componants like Virtuemart that are designed to be installed on Joomla cms websites, there are also a range of plugins for Wordpress websites for building your store as well as hosted ecommerce stores, they supply the hosting and software and some even manage your store for you, all though you will be paying for it.