From a link in the article:
For our purposes, we decided to define a tool as a material device that provides an advantage in accomplishing a task. That eliminated things like language and software.
We decided to exclude the traditional list of "simple machines," which includes the lever, pulley, wheel and wedge, since most other tools employ some form of simple machine--a hammer is basically a lever, and an axe is essentially a wedge.
We tried where possible to limit the list to handheld or easily portable objects, eliminating most heavy machine tools, like hydraulic jacks.
We also decided to eliminate complex machines capable of essentially running themselves. That means things like cars, windmills and computer networks don't qualify.
This excludes a few items I would have guessed, including knife (a form of wedge), wheel (specifically excluded), telephone (runs itself), and printing press, fire, boat (all three fail the portability test).
A few possibilities:
lantern
bow and arrow
ruler