Asklemmy

Knives.

About as low tech as it gets, even for modern knives that are pretty high tech in how they're made.

But it's entirely possible for a person to make a knife with nothing but tools they can make by hand, with no need for anything other than rocks as tools. I've done it, and it isn't like I'm some kind of super genius.

You can make slightly more high tech tools if you want, and make metal knives. The caveat to that is that you have to know how to identify sources for the metal in the first place, unlike stone tools where you can figure it out by banging rocks together until you find some that make sharp edges. But making an oven that can turn out low-grade materials is realistic for a single person to do.

But a knife, in its essence is just an inclined plane done to a very fine degree. Doesn't get any more low tech than that. Mind you, there's plenty of complexity involved in all of the basic machines like inclined planes, but that's more about understanding them than using them or making them.

Knives are mankind's most important tool. They were among our first tools, and it can be argued that they were our first manufactured tools. And we still use them regularly. Some of us use them every day, multiple times a day.

That's a lasting technology in every degree of refinement.