- to refer to a set of technologies that together form the future Open Web Platform. These technologies include HTML5 specification, CSS3, SVG, MathML, Geolocation, XmlHttpRequest, Context 2D, Web Fonts (WOFF) and others. The boundary of this set of technologies is informal and changes over time.
- to refer to the HTML5 specification, which is, of course, also part of the Open Web Platform.
Although it would be great if people used one term to refer to the specification and another term to refer to the set of specifications, in practice people use the term both ways.
Learn HTML5 from W3C
Microsoft offers Visual Studio Community version for free. But if you are looking to design an HTML website, not an asp.net Web Forms or MVC application, it won’t offer you anything other than what EW4 offers, and will be far less easy to navigate since it really is for asp.net, primarily.
The only competitor is Dreamweaver, which is not free (quite expensive, now, actually), and has its own list of foibles and critics.