The Sass vs vanilla CSS battle has been going on for some time now. For those new to the party, Sass is CSS, plus nested rules, variables, mixins, and more, all in a concise, readable syntax. When coupled with Compass, things can get pretty interesting.
Well, the developers of Sass have been wanting to go more mainstream and have realized that the Sass syntax, while there are many who love it, may not be for the everyday mainstream designer.
SCSS is a CSS-style syntax for Sass. It will have the same power and semantics as Sass, but the syntax won’t be whitespace-sensitive; instead, it will be a superset of CSS, or as close as possible. It’s currently in heavy development, but should work well enough that it can be used from the command line or via the Rails plugin, although not all the features are there yet.