Just found out this online mapping tool.
It's very similar to (and probably inspired by) Grid Cartographer, though much more primitive and not really a competitor.
However, one thing it does right is how it displays note tools.
You hover the mouse cursor over a map square with a note, and a text balloon appears.
It's a) nicely rounded and shaded, not just a rectangle, b) located right above the targeted square, not in the top left corner of the app.
Could you please incorporate these improvements into GC if it's not too much trouble? They are probably minor in terms of code, but they would be a nice improvement for map readability.
It doesn't hurt to ask!