Would that include box cutters? Ohh, the irony...
Indeed, but I will point out that it was not really the box cutters that enabled the 9/11 hijackers to succeed. It was their knowledge of airline protocol for handling a situation like they created. On 9/11/2001 the protocol was COMPLY with the demands and let the experts handle the negotiations on the ground.
In their infinite wisdom they did not consider terrorists who wanted to turn planes into weapons and were intending to die in the process. Note "intending" not "willing" to die. Big difference. The govt. and the airlines were caught off-guard and that is what allowed 3 of the 4 planes to hit their targets.
Had the 4th plane been on-schedule, it would have succeeded as well. But the people on the plane, once they understood what these hijackers intended, overpowered them and, unfortunately, the plane crashed in the process.
But how many people can a man with a box cutter hold off? Yes, you can be injured with a box cutter, but it takes some time and work to kill with one. What would happen today if someone pulled a box cutter and tried to hijack a plane?
So the real weakness that Mohammed Atta and his friends exploited what PROTOCOL. They knew EXACTLY what the flight crews would do and took advantage of that.