Observable launched a couple of weeks ago. As far as I understand, it’s sort of like a mix between CodePen and Medium where you create "notebooks" for exploring data, making nifty visualizations.
Check out this collection of visualizations using map integrations as an example. The entries are not only nice demos of the libraries or technology being used (i.e. D3, Google Maps, Leaflet, etc.), but also make for some interesting infographics in themselves.
In a note about this interesting new format, founder Mike Bostock describes a notebook as “an interactive, editable document defined by code. It’s a computer program, but one that’s designed to be easier to read and write by humans.”
All of this stuff riffs on a lot of Mike’s previous work which is definitely worth exploring further if you’re a fan of complex visualizations on the web.