Capital Wasteland is the name of a mod in the works for Fallout 4 that adds all of Fallout 3 to the newer game. It’s a complete overhaul project that’s occasionally run into legal snags, but the team behind it is still hard at work, and now they’ve produced a new trailer showing some feral ghouls (and other beasties) in some select locations from Fallout 3.
https://www.pcgamesn.com/fallout-4/capital-wasteland-mod-feral-ghouls-trailer