StreamBuilder is an automated build environment well suited for HTML, CSS and JavaScript prototyping. It runs on the (streaming) build system Gulp and comes with goodies like the SASS CSS extension language and the Nunjucks template language.
By working in the /src directory all of your changes are piped and rendered to the /dist folder.
/src/scss->/dist/css/src/js->/dist/js/src/pages->/dist//src/img->/dist/img- It even refreshes your browser on every change!