Side-cutting.
Rösle tin opener.

This is such an unusual gadget that we are adding it to our range of recommended appliances. Tins with a seamed lid are opened from the side, directly beneath the seamed edge. Place the stainless steel hoop on top of the tin and allow the cutting wheel to engage at the side. When the wheel is turned forward, the top is removed. The cutting wheel does not come into contact with the contents of the tin and the top of the tin is surprisingly blunt and smooth, providing less of a hazard. The top can simply be lifted off and replaced again if necessary.