The top Content Management Systems that are widely in use are WordPress, Joomla and Drupal.
WordPress is widely used, but it is very likely that for a website such as Apple's, they could have used Drupal - there is more that you can do.
You need to search for themes and WordPress.org has many free themes that you can search for inside the installation itself. Drupal not so many, but you can do a search.
However, people use themes and adapt them for what they want and it is highly likely that Apple would have done this - you get a basic theme and you then adapt it for your own use by altering the colours - this means that you have to get in and alter the CSS code of the actual theme itself.
You also extend the content by adding what are known as Plugins in WordPress and Modules in Drupal.
I would suggest that you do some reading up about Content Management Systems and how they work before you install one of them. Drupal.org, WordPress.org and Joomla.org.