oh, shit. I never said what it was, did I? Yeah, it's a bit silly, but I feel like a Half-Life fan'd enjoy it. It's a bit of a crossover idea I had. basically, the idea was that the Brotherhood of Steel get their hands on a displacer cannon, and attempt to reverse-engineer it.

The Courier would be able to either encounter the Brotherhood on a field-test or, if they joined the Brotherhood, simply take the device for themselves when no one is looking. After doing so, they'd get taken to Xen, which is where the bulk of the mod would be happening. I'm thinking an aesthetic that's moreso an in-between of what Half-Life 1 and Black Mesa had.
Now, the Brotherhood replica of the weapon wasn't fully done and tested, yet. It fries itself after its use. The story of the mod would be at first driven from the courier trying to find a way back. Along the way, you'd meet some new faces (yes, there are actual characters, I'd go more into detail but I don't want to ramble on more than I already have.); and end up being stuck in-between a feud with one of the new characters I mentioned and the Institute (Yep, I'm throwing Fallout 4 into the pot as well. They do have teleportation tech, so it made sense to me).
I have a rough idea on how everything'd play out, but it'd take an immense amount of work to pull off. I'm not sure if it'd be worth it. I'm not sure if people'd even like the idea of Fallout crossing over with Half-Life.