observablehq:
https://beta.observablehq.com/?utm_source=blocks

5 open-source tools:
https://www.kdnuggets.com/2018/07/5-favorite-open-source-visualization-tools.html

http://datavizproject.com/

https://frontendmasters.gitbooks.io/front-end-handbook-2017/content/tools/charting.html

https://keshif.me/demo/VisTools

https://processing.org/ - Build interactive visualizations interactively. Great O’Reilly book, Visualizing Data

leaflet - maps
http://leafletjs.com/

See the section on cartographic tools.
https://www.mapbox.com/ -

See the section on cartographic tools.
http://www.qgis.org/en/site/forusers/download.html -

Heavy-duty toolkit - used in the medical, chemical, and physical research.
http://www.vtk.org/ -

https://www.toptal.com/opengl/introduction-to-opengl-a-quick-tutorial