HAK: Hideaway Knife
A couple of years ago, a good friend gave me this as a present: a HAK or Hideaway Knife.
He told me: Just keep it, as a last resort weapon. And that's what this is, a weapon. The HAK is not a utility knife. It was designed and built to be used in a defense situation. The concept is that you can place two fingers on the handle, using it as an extention of your fist. Like a tiger claw. The good thing is that while the knife is in your hand you still retain the ability to grab things and use your hand perform locks on the attacker and other things.
It is a great little defense tool. Here you have more pictures.