Here's some feedback for the product itself.
- As noted by other HN users, the selection behavior is unintuitive for me. I read the comments here before trying it, so I understood exactly what to do. But as a naïve user, I wouldn't think that double clicking went 1 level deeper into containers, I would think that it went directly into whatever I'm clicking. For instance, if I click into a text box that's 2 containers deep, it would go directly into the text. I know other programs solve this by having a select tool and a "direct" select tool, although that might be a bad solution here... either way, I think you might want to think about the UX on that more.
- When editing text, I see a red circle with a minus inside. I would assume as a user that it removes the current element, but it doesn't seem to do anything when I click it. Very confusing for me.
- Adding links seems a bit confusing. I selected a text element inside of a container, clicked the chain icon to add a link, and then typed "www.google.com". I didn't see any confirm button, so I pressed the "enter" key on my keyboard. It seems the link was added, but the text didn't turn blue the way I would expect, and the "add link" interface didn't disappear as I would expect. I think just adding a confirm button that when clicked hides the add link interface (and goes back to the one with italic/bold/link/etc) would make it more straightforward.
- Adding an input element didn't seem to work at all for me. After double clicking the "input" option in the element list, I wasn't given the option to select its location like I was for all the other elements.