I found this nice tool on Twitter (exactly where escapes me) and I had tinkered around with it and found it very useful. I haven't used it in production or development when it comes to my projects, but I know that someone could make great use of it somewhere, which is why I am posting this.
Typetura is (taken from the website) a fluid typesetting tool. Select a breakpoint and then use the style panel to add style to your page. Simple as that.
You can edit, add text (paragraphs, headings, lists and blockquotes), and tinker with the fonts with many CSS font properties. Take it for a spin, it's still in beta and the creators, Scott Kellum and Sal Hernandez, are still adding features and killing bugs. They're also taking questions and feedback. The info for that is right on the website.