The freedom to mod Fallout 4 includes the ability to see in-game characters with their clothes off.
Deviant Art user ArtoftheBody has a released a nude mod for Fallout 4. The mod does what you’d expect, replacing game textures with ones for nude characters.
Curiously, it appears it only does so for female NPCs. Such a shame.
You can learn how to use it and download it from here.