I used a combination of scripting and modding tools to make three custom traps for my Fallout 3 mod, It Belongs in a Museum!
This trap consists of a series of squarish platforms, each with a very thin trigger box above it.
When the player steps onto the platform, they hit the trigger box, which activates the trap. In the above example, aaNU43a, aaNU43b, aaNU43c, and aaNU43d are Static Mesh objects (each square platform is actually composed of four separate Static Mesh objects). The script disables those objects, and plays a sound effect as the player falls below. The trigger also has a variable that ensures it only fires once.
A kill volume on the ground beneath the platform finishes the job.
This area has a series of faces in the walls that shoot arrows (or rather Rail Spikes) at the player. The trap is triggered automatically once the player enters the room.
Once the trap has been triggered, the only way to disable it is by shooting the override switches found throughout the room. This trap is run by a script that is similar to the Pitching Machine script.
The faces shoot a custom projectile that deals a significant amount of damage to any player who tries to run by. The projectile is incredibly accurate, and has a spread variation of zero.
This trap is run by a modified version of the pitching machine script. Once the trap is triggered, it fires an unlimited barrage of custom Railway Spikes.
These Railway Spikes deal enough damage to kill most players in one hit, and their Spread is reduced to 0, so they fire in a perfectly straight line.
The only way to disarm these traps is to shoot the switches found throughout the room. When shot, the switch disables the trap it is linked with, and then disappears.
This trap is activated as the player leaves the final chamber after getting the treasure. I use a condition to ensure that the boulder only fires if the player is at the appropriate stage in the quest line.
This trap is run by a modified version of the pitching machine script. It fires one custom boulder projectile.
The boulder projectile uses a custom model, which was created in Max and imported into the engine using a variety of plugins and exporters supplied by the Fallout 3 modding community.