One of my favorite and most heavily used apps iA Writer just got a big update with its 1.4 version release today:
Inspired by our deep experience designing for the web, we’ve given Writer for Mac a responsive design, changing the font size based on window width. This maintains the text’s typographic proportions, zooming in and out without reflowing the text. I don’t know why it took us so long to find this obvious solution. However, given that no one else has done it, the simplicity of this solution is perhaps not as obvious as it seems in hindsight.
After playing around with the update for a few minutes I can’t find an immediate need for the three different breakpoints iA Writer offers; 95% of my time I feel like the largest font size/width is optimal. We’ll see how that evolves over time.