Hi there! Currently the GUI Editor is in a very very early alpha. We haven’t formally announced it or put the URL anywhere in documentation because it is in such a rapid moving state.
Based on the last couple of days a couple of people have found the link and have been playing around with it which is exciting and cool to hear about.
For transparency here is the link If you’d like to play with it https://gui.babylonjs.com/ Please keep in mind however that is still in active development with a lot of things already planned and still yet to come. We’re targeting an formal alpha version in the coming months, and a beta in the fall.
That being said I if you’d like to follow along with dev updates I encourage you to follow me on twitter.