Hitman: Absolution's contracts mode will let you craft new assassination missions using single player settings. Any NPC can be elected as a target. Once you've laid out a challenge, you can share it online and challenge Agents all over the world to do it in the fastest time they can.
IO Interactive have released an 18 minute walkthrough video to show exactly how it'll all work, which also shows off a bit more of the single player levels that have appeared in previous trailers. That means we get to see Agent 47 distract a corridor full of cops using a hippy disco. Even flower power can be used to kill in Hitman.