Sass.js
Sass parser in JavaScript. Have a look at the Interactive Playground to play around with compiling SCSS to CSS in your browser.
This is a convenience API for emscripted libsass (at v3.5.5). If you're looking to run Sass in node, you're probably looking for node-sass. Sass.js and node-sass should generate the same results.
A fair warning: minified the worker weighs 3.5MB, gzipped it's still 750KB. If you're on NodeJS, please use the (considerably faster) node-sass instead.
You may also be interested in giving Dart Sass a shot.
Documentation
Who uses Sass.js
Sass.js is used in the following tools:
Authors
Credits
License
Sass.js is - as libsass and emscripten are - published under the MIT License.