This tool has an admittedly narrow application, but I’ve found it quite useful for working in a datacenter. It’s a ruler that’s scaled to count spaces in a computer or audio rack, which measure a standard 1.75 inches, making quick work of documenting racks or figuring out if there is enough space in an existing install.
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.