What are the most interesting uses of SVGs you've seen?

Here's an SVG that works as a functioning calendar

I am not sure if this was anyway practical but I found this project interesting.

Google font to SVG

As the name suggests, it converts Google fonts into SVG :)

well for everyday's tasks when you're making a new website , sometimes you want to make a complicated shape, so you try to do it with css (:after , :before and tricks here and there) which can be easily implemented with svg which will be responsive as well and it won't ruin the whole page on a different viewport.

Data visualization is something really interesting that you can do with svg and javascript, D3.js is a javascript library for data visualization using SVG and canvas as well, it's super cool even when you combine javascript and svg even without d3.

you can watch these awesome talks about svg by the amazing Sarah Drasner , Sarah Soueidan and others

does github.com/rionmonster/borbs count?

roughjs.com/ - Allows you to generate SVGs that have a "sketched" look.

I use in a multi tenant webchat, usually each tenant has it's colours with svg I can override fill property and customize easily any icon.