less.js is the next evolution of LESS, eventually, it will become LESS 2.0. less.js is a complete rewrite of LESS in JavaScript, and will be able to run directly in the browser, as well as on the server, with node.js.

The latest builds are in the dist/ folder.

var less = require('less');

less.render(".class { width: 10px * 2 }", function (e, css) {
    sys.puts(css); // .class { width: 20px }
});

bin/lessc style.less

Get the pre-built version from the dist/ folder, and include it as such:

<link rel="stylesheet/less" href="main.less" type="text/css">
<script src="less.js" type="text/javascript"></script>

Note the rel="stylesheet/less" for all stylesheets you want to parse with LESS.

In node:

$ npm install less