Are you going to argue that it is? Is GRUB merely a "tool" for booting your computer? Is libc a "tool" for exposing OS-provided functionality to software? Is GNOME a GUI "tool"?
Ok clearly you think the rest of your argument is obvious, but I'm going to be dense and say "yes", those are tools. Just as the Linux kernel is a tool for managing the various resources of the system. Maybe it's the word "merely" that's tripping things up, but I don't see how any of these things fail to fit the word "tool".
It would be easy to argue that most software fits the "tool" label. As far as I know, rms objects to describing GNU as a set of "programming tools" or "development tools" as he (reasonably, in this case, I think) finds those labels unfair. GNU software is required for any operating system using the Linux kernel, as far as I'm aware, and those systems are not limited to programming or development.
