Lightermail.com allows you to "control your inbox - decide how, when, and from whom your email is delivered". My role with Lighermail was to establish the brand, then design and build a user interface that could support the application.
The design is somewhat minimal so the users can focus on the task at hand - either converting to a user, or actually using the application. I used a mostly greyscale colour scheme with bright colour highlights for UI controls, and mixed up the typography and white space to keep things clean looking.
I built the front-end using HTML5 and CSS3 (SCSS) on top of a Backbone.js/Python back-end. Media queries make the site responsive, and a pinch of CSS3 transitions to round things out.