Typecast allows you to design and experiment in your browser with real content and test over 23,000 web fonts, including the most popular ones that include all weight families. It also allows you to compare font combinations to see what works.
Typecast lets you build a clean and well-detailed HTML and CSS as you design, embed fonts and test your designs without setting up kits.
You can also design a vertical rhythm, creating a baseline grid with just a click, then set your rhythm without crunching numbers. Another feature of this is that you can focus on finer prints and create project-wide changes quick without the use of screenshots and recaptures.