[smokel]

This paragraph seems pretty clear to me:

"Glamorous Toolkit is the Moldable Development Environment. Moldable Development is a new perspective on programming through which we create custom tools for every development problem. We find that this ability changes the very nature of programming."

It's an IDE that lets you easily create tools for experimenting with your code.

[Taikonerd]

And, IIUC, a debugger that lets you define custom views for interesting data? For example, in the "GtLudoGame" image (the first image in the post), the rightmost picture is some sort of custom debugging view for a game state -- so you can visualize it directly as a board state, instead of as a dict or list or whatever.

[seandenigris]

Yes. That said, it took me a while using it to figure out that one non-obvious key feature here is that “easy” means that they’ve made it cheap enough where one automatically changes their behavior and actually does create ubiquitous custom tools, where in other systems extension is more an afterthought, or at least distinct from “regular programming”