There are great and popular CSS preprocessors like SASS and LESS.
Myth is an other one which allows us to write pure CSS without having to worry about browser support, or even slow spec approval.
It simply functions like a CSS polyfill but we can still use variables and math functions.
Semantic is an exciting new front-end framework that comes with a set of specifications for sharing UI elements between developers.
The vocabulary used (for classes and IDs) is much clear compared to alternatives which lowers the learning curve.
There are styles for many HTML elements, UI elements and scenarios (buttons, forms, tables, accordion, navigation, commenting..).
LESS is used as the CSS pre-processor and Semantic is currently in a pre-release version but planned to be improved with much more stuff.
Web designers/developers who write client-side code with a language that needs to be compiled, usually lose some time going back and forth with their editors and the compiling interface (usually command line).
If you don’t already have a setup for auto-compiling, Koala might be what you need.
It is a desktop application that works on Windows, Mac + Linux and can compile Less, Sass, Compass + CoffeeScript.
Koala can compile the files manually or automatically once they are changed and compresses them.
Also, it is possible to set different options for each file to be compiled.
KineticWing is a free IDE that is lightweight, portable and works on all major operating systems (Mac support is mentioned to be coming soon).
It is not a complicated IDE but more like a smart text editor with modern features.
These features include support for Sass or Less (with built-in compiler), HTML5-CSS3 or CoffeeScript.
KineticWing is supporting server-side languages as well and more of them are being added within time.
The editor is not yet perfect, it is in beta status, but the features and roadmap are very promising.