Say you have two things: a perfectly good hand, and a brilliant inventor for a grandfather. One day you stumble across a blueprint for an amazing-as-hell robot hand meant to replace an arm-stump. Wait, you have three things: the hand, the grandfather, and a saw.
http://www.teamfortress.com/images/posts/gunslinger.jpg
The final day of the Engineer Update unveils the Gunslinger, a mechanical stump-mounted monstrosity; "Thunder Mountain", the most awesomely named of our Valve-created Payload Maps.
Stop reading. Go play!
