They wrote a great paper explaining their "Unit Visualization" concept/approach: https://www.microsoft.com/en-us/research/wp-content/uploads/...

IIRC their engine used to be their own in house WebGL code, but according to their GitHub ( https://github.com/Microsoft/SandDance) they are now using Deck.gl (https://deck.gl/) for rendering and Vega for chart logic. I do think it's not designed to be used as a library though but a complete studio like environment.