By now, I'm sure you've all heard of the Pixar Theory, the notion that all Pixar movies exist in one cohesive timeline. It's a pretty wild theory, but Pixar isn't the only company that finds itself subject to wild fan speculation.
As fans have discovered in Fallout 4, there's an experimental plant that could link the post-apocolyptic world with another of Bethesda's massive RPGs, The Elder Scrolls V: Skyrim. Detailed by Kotaku, the source of the theory stems from an experimental plant found aboard the Prydwen, the airship commanded by the Brotherhood of Steel.
It is in the research station of this ship that you'll find an "experimental plant" quite similar to that of the "Nirnroot" found in Skyrim. Although the site acknowledges this could just be a case of Bethesda reusing assets, there's a few details in the game that suggest more to the story.
Next to the plant is a computer terminal with entries labeled as "NRT," perhaps shorthand for "Nirnroot." The plant is described similarly to the Nirnroot in Skyrim, with one log even explaining how the experimental plant is found "at the mouth of the river." In The Elder Scrolls, lore says that Nirnroot "grows only by the water." Over on Kotaku, you can read the full log entries which provide shaky at best descriptions linking the two worlds.
Similar to the Pixar Theory, I doubt this has any true merit to it aside from being a fun easter egg. But it's still a pretty cool find, and just one of the examples of how intricately detailed the world of Fallout 4 actually is.
Speaking of easter eggs, have you seen the crazy Alien reference in Fallout 4?