It's a wet-erase mat

Heard about it through Reddit ads, and am currently using it instead of Roll20 because of the simplicity of the whole system and the current reliance on an online alternative. As you’ve pointed out in some of your blog posts, the simplicity of a basic white board (that also has features like rapidly filling blocks) is super nifty given I’ve been resorting to a chalk/whiteboard in my home games anyway.

Roll20 is great if you want a million features, but neither me nor my players really need integrated character sheets, automated rolling, super fancy tokens, and all of the stuff that comes with their system. It takes too long to do basic things unless you spend a bunch of time mastering their interfaces. A simple colorable grid with movable tokens was all I wanted, and this does exactly that.

My players also seem to be big fans.