Carto
I have built a small sub-site for my digital cartographic experiments called carto.liquidx.net.
It's a helpful little container that I can put many of my random thought experiments about mapmaking and cartography. I've moved a few of my earlier maps in to there - my Japan Train Maps and Hokkaido EV Charging Map.

There are quite a few new experiments in there, but just even some basic ones are fairly fun. This one is producing contour maps out of terrain data of several providers.

It is nice to be able to mess with contour maps on the fly and experiment with this on my favorite mountain.