I've been working on a similar web builder with Entomic - https://www.entomic.com https://www.entomic.com - that lets you create sites and get live previews acr

I've been working on a similar web builder with Entomic - https://www.entomic.com https://www.entomic.com - that lets you create sites and get live previews across different browsers and devices as you develop. It's a little rough still, but it does make responsive development a bit easier.