On a meta note, I bought a box cutter (a nicer-looking version with wooden handle) [1] so I can dispose of all the boxes we are getting these days.
And for opening boxes, I picked up one of these key/cutter tools. [2] It's plenty sharp for cutting the tape on boxes, but it's much safer than a box cutter, so other family members can use it. Each of them was about ten bucks.