Adobe offers a 30-day, free trial of Dreamweaver CC, as of 2015. To download, navigate to Adobe.com, click Menu on the top right of the page and choose Dreamweaver in the Products tab. This trial requires users to create a free Adobe ID and download the Creative Cloud application.
Other than the trial, Dreamweaver can not typically be downloaded for free legally. However, there are a number of free alternatives to Dreamweaver, such as Quanta Plus and Aptana, that offer similar functionality. Both of these are open-source and have similar support for various web coding languages. Quanta Plus in particular resembles Dreamweaver's environment and offers a similar what you see is what you get editor. Aptana does not offer a WYSIWYG editor but is otherwise largely comparable to Dreamweaver in functionality.