As you requested feedback, it's dead simple and I like that. Speed and low friction is super useful in a lot of situations.

I have just some "bugs" I guess (Windows Chrome):

- Can only add text to a box immediately after selecting it. Move it first, then cannot add text. Probably should be a blinking insert symbol to indicate when you can edit text or not, as this would at minimum make the state "discoverable". Personally I feel a lot of people will try to double click to edit text.

- Backspace deletes boxes but "delete" does not.