In this post, I'm going to talk about programs you can design websites with on a fundamental level i.e. using HTML, CSS and JavaScript. It's possible to build a website using CMS technology without requiring programming skills, but there are limitations.
Dreamweaver is the best program for website design
The best program for designing a website is Dreamweaver hands down. Many WordPress developers Use Dreamweaver to create plugins and theme. Most of the HTML themes still being used today are built by and for Dreamweaver users. There was a time when Front Page was very popular. Front Page was an attempt to create a very capable WYSIWYG HTML editor, but it failed to keep up with browser compatibility trends and proved to be too limiting overall. Dreamweaver splits the program into two windows, a WYSIWYG editor and a source code view. The WYSIWYG editor is for convenience, but the source code view is where 60-90% of the designing work has to be done.
Dreamweaver is currently owned by Adobe and Dreamweaver can be purchased from their website as part of a program package recurring subscription plan. if you're not sure if you want to purchase Dreamweaver you can download a free 30 day trial here.
This probably isn't legal, but I was able to buy a laptop and reformat it every 30 days to restart/re-install my adobe trial programs(including Dreamweaver) each month.