The Tableau algorithm is patented. In particular, the algorithm that chooses the type of the chart depending on the properties of the data. It was developed under the name Polaris at MIT (?).

A few patent applications were accepted in the US and declined in the EU.

This is based on graphic-walker which is based on vega as far as I see. It would be interesting to see if vega is different enough from Polaris/Tableau.