A knife is the oldest known tool that is made by human hands, and not found as-is in nature. It is also the tool that makes all other subsequent technology possible.
There are a limited number of things one can make without a knife, using unmodified rocks as hammers and abrasives - to separate plant fibers to make a rope or string of some sort, or to scrape away wood to make a pointed stick. One can use a pointed stick to dig for roots and edible creepy-crawlies, or use it as a crude spear.
Recently they've dug up some wooden throwing spears, from a peat deposit in Germany, that are 400,000 years old - Homo Erectus vintage. Traces of knife making go back now about 2,500,000 years. There is now one chimpanzee, named Kanzi, who, with lessons from an anthropologist, is making some very crude stone knives.