There is a place, a awesome place called the Nexus, which can be found Here --> http://www.nexusmods.com/fallout4/?this place has thousands of mods already for fallout 4. Even more for fallout 3, and a metric ton for fallout New Vegas.
So if you have not heard of them before, go and check them out. If you do not know how to mod your game right now, you can do a youtube search for Gopher FALLOUT 4: Enabling Modding for PC I would link straight to the videos but I do not know the policy on linking to youtube here.
Lastly, if you really want to play fallout 3 but do not like how it crashes so often, there is one more place for you to check out, its called tale of two wastelands You need to own legally I might add, both fallout 3 and fallout New Vegas, but via modding you will be able to play fallout 3 on fallout NV engine. Thus making it far more stable. One piece of advise though, as tale of two wastelands is a big mod read there guide, fully.
Any rate. Happy gaming.
*Edit* Sorry moderator did not see there was a sub category just for mod talk

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