https://orteil.dashnet.org/taskmaster/
If you click on empty background, a new box comes into being. You can configure/turn off the box's timer, edit its title, set an emoji and write notes on it. You can change its color, or grab an image URL to make that the background. Boxes can be resized (fitting the bg grid).
I... I dunno man, I found this on orteil's tumblr and figured "the Cookie Clicker guy hasn't steered me wrong yet" and went to investigate. I'm not sure it's a functional producitivty tool for ME, but nevertheless I will hold it up cheeping inquisitively.