"Origami Stationery offers fun folds for dressing up your correspondence. There’s a variety here, in terms of what functions the folds will serve. There’s a trapezoid note fold, for instance, that will go in the corresponding trapezoid envelope. I’m pretty sure the trapezoid note would be mailable as-is, though, as long as you seal it shut first. Others would need to be tucked inside a regular envelope. This is one of my favorites."