As someone who just had to generate these for the first time ever, I was surprised and disappointed at the current products available. I'll definitely give this a try. It looks fantastic!
Hi. There is just no way to manipulate images without JS, with pure html/css. Even if we wanted to. Although, I wouldn't be surprised if someone does it.
What do you mean by desktop apps? To include desktop apps in our mockup examples? Or to create a stand-alone application for Mac/Windows? If you show us examples of what you mean, it would certainly appear on our todo list.
