AI knives were a type of throwing blades. They were passive-telepathic, made of trintillium and filled with micro-gyros. When thrown, they would adjust themselves to hit the target, provided the thrower had the target's image in their mind. The knives would then return to the thrower's hand.
Torchwood Three had several AI knives in its possession, which Jack Harkness debated using against the assassins from Hokrala Corp. He later used them on a Weevil to stop it from attacking a human. (PROSE: The Undertaker's Gift)