Emmet (previously known as Zen Coding) is a web-developer’s toolkit that can greatly improve your HTML & CSS workflow:
Basically, most text editors out there allow you to store and re-use commonly used code chunks, called “snippets”. While snippets are a good way to boost your productivity, all implementations have common pitfalls: you have to define the snippet first and you can’t extend them in runtime.
Emmet takes the snippets idea to a whole new level: you can type CSS-like expressions that can be dynamically parsed, and produce output depending on what you type in the abbreviation. Emmet is developed and optimised for web-developers whose workflow depends on HTML/XML and CSS, but can be used with programming languages too.