Again something that rules as to being simple, functional and aesthetic: the list-keeping app called Clear. Maybe not an obvious choice to stand by, in a world that offers more and more options. But I understand it and even more so after having tried this app for a while.
The whole idea revolves around simple feedback in the form of gradient colours, vibration, and sounds. A combined visual, tactile and auditive experience, which stimulates basic human senses in a varied and still holistic way. As a surprise, quotes also show up, but elegantly. I think it makes it rather fun and almost musical to make and maintain such a simple thing as a list.