Fifty years past, there was a place where not even the great Sun-Goddess Celestia had power. In a place where only earth ponies and unicorns lived, the great evils of uncontrolled scientific inquiry were proven, and the dangers of ambition were made clear for all there to see.
This is the story of a pony who stumbled across the great city of Euphoria and became embroiled in the greatest power struggle Equestria never saw.

This isn't a pure crossover.

A lone stallion, trudging through the wastes of the great Ponave Wasteland, comes across a young pegasus mare. He helps her against his better judgement, not knowing how his life has been changed forever.

Set 50 years after the end of Kkat's Fallout: Equestria. I'm taking many liberties here, mainly that the Pegasus Enclave has been defeated and they have been, warily, accepted into the normal post-apocalyptic pony society.
I shall be drawing on my experience playing both Fo3 and Fo:NV. Expect New Haygas/New Neighgas (Dunno which one I'll use yet) to appear.

The concept was based, in the loosest sense of the word, on Iron Savior's Faster Than All