This was launched in 2013 (previous discussion - https://news.ycombinator.com/item?id=6470426)

The basic conclusion was that it's a tool for creating ads.

Thanks for the heads up!

Thanks! Burying as dupe.

So I checked this out back in 2013, and it has gotten significantly better. For one, it doesn't include a giant script at the top of each document this time around, so that's a major plus. I haven't used it very extensively, but I have high hopes for products like this. Game engine map editors have been around for decades. It would be really cool if we could create tooling that is able to spit out complex web app designs in the same way.

Less of an "web designer" and more of an "ad designer"

Ad designer – that's what we've been trying to build at http://tweenui.com/animator, and I'd love to hear how GWD users think we stack up.

Is there any documentation?

Docs: https://support.google.com/webdesigner/#topic=3178270

Groups: https://groups.google.com/forum/#!topic/gwdbeta/

I'm not sure if this is the type of documentation you're looking for, but here's a link to the relative Help Center:

https://support.google.com/webdesigner/#topic=3249465