A cool tool can be any book, gadget, software, video, map, hardware, material, or website that is tried and true. All reviews on this site are written by readers who have actually used the tool and others like it. Items can be either old or new as long as they are wonderful. We post things we like and ignore the rest. Suggestions for tools much better than what is recommended here are always wanted.
Kik-Step Rolling StoolI have used a Kik-Step rolling stool for at least 15 years. Its design is simple and brilliant. Without any weight on it, you can roll it around easily. But with a bit of downward pressure, the round bottom rim hits the floor and it becomes a stable stepping stool. The slanting body design helps it avoid damaging walls and bookcases.
These were ubiquitous in libraries when I was growing up. In my office, it triples as an ottoman for stretching, a seat for when the couch overflows, and a short step for reaching high shelves.
They come in gobs of colors. And having been around for 50 years, there's a robust aftermarket for parts.