FluidStance, a company that sells balance boards, also sells this unusual object:
Called Slope, it's a $60 bent steel sheet that's been powder-coated for dry-erase functionality. It's magnetic, and a channel at the back is meant to hold the eraser. It also holds the included silicone phone holder, and has a slit in it for a charging cable.
The company writes that the object "is here to help reduce your eco-footprint by eliminating disposable paper notes."
You can slide your keyboard under it, which I suppose would be useful for those of us who eat lunch at our desks and are used to cleaning crumbs out of keys.
As a laptop user this isn't for me, nor is my desk deep enough, but user reviews (assuming they're real) are surprisingly effusive.