“Bone folders” made of real bone are classic, but I prefer a plastic one. The one I use for making crisp folds in origami, for bookmaking, folding cards, and paper construction is molded to the hand for extended ergonomic use. It slides super easy with no trace on paper. Sharp point, makes a really crisp fold. Lasts forever. Inexpensive. If you work with paper, you’ll want one of these.
A cool tool is anything useful that is superior to comparable items. If you think this tool is inferior suggest a better one. You are welcome to insult a tool, but comments containing insults to individual people will be deleted. Corrections of fact are always welcomed, if stated politely. Recommendations of better tools are dearly wanted and may be elevated to the front page.