[contr-error]

Thanks for sharing, looks really nice. Way less verbose and more intuitive syntax than PlantUML. Also seems to drop some vestigial UML aspects, like those default icons in the top right of PlantUML boxes (although I don't really grok UML). Title is somewhat ambiguous, since PlantUML is open source as well.

I have a standing Google alert for UML threads, because I've been looking for a long while for a good resource on what makes a good diagram. Not how to make it or what to make it with; like a Tufte for diagrams... Anyway D2 seems to make it easy to make clean diagrams.