Joomla! has a vast amount of extensions (aka modules) that are available and a great majority of them are available as open source (free). They plug right into Joomla through the administration back end "module installer" page.

• Joomla has a free e-commerce solution called "Virutemart", which can either be installed as an extension to Joomla, or you can download a Joomla e-commerce addition with Joomla + Virtuemart already packaged together.
• Joomla also has a free forum known as "Fireboard" that easily integrates with your joomla installation. There's also many bridges to exsiting PHP based forum software such as "Simple Machines Forum" or "phpBB" that can be installed to tie in your joomla site with one of these.
• Joomla has many ways to display your media content such as picture galleries, movies, or podcasts. One nice free gallery solution is known as "RSGallery".

Everything that has been mentioned here has been tested with success at Applied Innovations.