Look promising, but just logged in and poked around and couldn't figure out how to get elements on the canvas. Or do much of anything. Some of the interaction design seems quite odd and difficult to use (eg. all the sidebar accordions open on hover rather than on click. And clicking on elements in the "insert" dropdown doesn't insert them.).

Apologies for jumping to critical feedback! Rough prototypes are rough for good reason ;) Glad to see more of these GUI builders popping up and think this is a worthwhile avenue to explore. But might be worth spending a bit of time looking at interface design best practices. And/or getting a designer to come advise on the project.