The free version of Portia Party Dress. It includes one length option (knee length), and pattern pieces & instructions for knit fabrics only.

There are two styles to the back. You can either have it, so the back is completely open to the waist, or  stitched half way up the back and then open to the neck. The back fastens with either a ribbon or a  thread loop around a single button. Sizes XXS to 5XL.