It includes a collection of traps, torture devices, killing machines and creepy locations (see videos, the “overview”). Here’s a short description (and screenshots) of each one:
Spiky chasm of death. Bring the prisoner on the chasm, then shove him down! A spiky death awaits. [1, 2]
Lion pit. Hungry lions wait for their dinner, don’t forget to feed them regularly. (see videos) 
Creepy bridge with spikes. Your prisoners may fall. It happens. 
Cage of burning death: order your prisoners to enter the cage. Then use the lever to light the fire, or turn it off. Watch them shake and cry! Eventually they will die, so pay attention to their health if you want to play with that prisoner another game… Or just let them incinerate. (see videos)
Questioning chair: you can order your prisoners to sit on the chair. Then, you can choose to electrocute them (little damage), burn them (little damage), or shock them to death. They will play a fitting animation and cry in pain. They won’t move from the chair as long as you don’t issue another command. 
I gotta say, this is kinda creepy. But then again, I used to chuckle with glee while playing that old game OIDS ( http://www.mobygames.com/game/atari-st/oids ) on the Mac, when, instead of saving the andr"OIDS" of the title, I’d gun them down and watch them die a fiery death. Ah, virtual sadism.
There was something like this for Morrowind (and probably Daggerfall and Arena too). Some people like to get medieval on their virtual critters. When I’m in the mood to “unleash the pain” in that game, I generally just slaughter everyone I can find with my massively overpowered lich character.
Way I see it, if people aren’t designing things like this, the modding community isn’t really trying to hit the boundaries.
edit: Shit, if I post one more time I hit 1000. What a waste!
There’s a difference between occasionally blowing away a store owner in Fallout and getting a chuckle out of it, and what this guy is doing with this mod. This is designed to let you torture people, over and over if you like, because torturing people is fun. Now with Realistic Torture Screams ™! It’s creepy, beyond creepy. This is not pouring airplane glue on a plastic army man and lighting it on fire. This is closer to capturing squirrels and torturing them to death.