This is a gore mod for Quake 1 to exaggerate and show-off with a lot more blood that every other Quake 1 mod has to offer :-)
Here you can see the new chainsaw (heck, every gore mod, no - every mod needs one)
If you wield it against an enemy with low health, it pretzels the enemy with a fast attack, which makes the target unable to act in any way but being in pain. That can even happen to larger monsters like the Shambler. Good way to take down a damaged foe without thinking about his response to your attacks :-)
More weapons will follow with the time.
But be carefull while you carve down enemies on low health, other monsters in the area might still be able to aid their brethren.