Prezi* presentations - Zoom reveal is the most interesting feature of Prezi

[0]https://prezi.com/product/

Not a website, but pretty wild: http://eaglemode.sourceforge.net/

Impress.js has been going strong for years and let you create zooming presentation decks with html and css.

https://impress.js.org/

The only example I can think of is Miro (formerly realtimeboard), but it doesn’t feel like such a stretch there, since it makes sense for their product.