I tried making a mod that improves the story (and adds a bit more cannon no matter what choices you make in the game) and gives you a second companion in the game.
Spoiler (click to show/hide):
The companion is the opposite gender and alignment then your character. The idea was that (s)he was your lover as your grew up. Some of the first that happened was like during the GOAT test, if you decided to do it diplomatically, your lover would attack the Tunnel Snakes anyways. Or if you decided to do it violently, then (s)he would voice his opposition.
Other things that would happen are the overseer being killed no matter what, and stuff like that. Then when you left the vault, the first open ended quest you finish makes him/her leave because they wanted to do the right/wrong thing. Then random encounters would make megaton blow up, caravans be killed, or stuff like that (assuming your good alignment).
Then at the end of the game, (s)he would become your companion during the last mission, then do the good/bad thing at the end (bad thing is pushing you in to activate the purifier in a horribly animated cutscene, then being killed by lyons).
But I never got it done, and someone on the nexus took up the idea and just did a companion without the alignment differences. Oh well.
The main idea was the ability to see all good endings, followed by the bad endings, thus seeing most of the content in one save.
"Thanks to your unfortunate life, I've found myself being more and more grateful!"
"Are you horny? Do you not want babies? Just watch porn!
They'll make you jizz in your pants, so others don't have to!"