Web design software... Dreamweaver and the likes, but that's just solid HTML/ CSS unless you fancy writing pages of Javascript or PHP code.
If you're looking for a web platform, which is already set up and has themes, templates, plugins and what not, then you want to be looking at platforms such as Joomla, DotNetNuke, WordPress and the likes.
You can quickly install Microsoft WebMatrix on your home machine and download them in an instant to test them out if you want to try different web platforms offline.