You can install the Node.js on your machine. It serves to run various applications that you can download on NPM, among them the Gulp.
Gulp automates various operations for you. Allied to Gulp-Sass, for example, you will be able to compile your SASS files automatically each time they are saved - the plugin keeps watching the directory where they are and reacts to modifications.
Already for LESS, you can use the Gulp-Less. The principle is the same.
The instructions for using Gulp and its plugins are on each page. They are just a few lines of script for each of them.
Just a warning: Node.js is already addictive on its own, but its combination with NPM leads to a one-way street :)