If your curiosity was piqued by my last post about Skywind, the fan-made mod that's merging classic RPG Morrowind into the world of Skyrim, there's a new 10 minute long video from the team that's well worth your time. In it the full breadth of the project is explained, and unsurprisingly it's pretty damn impressive.
It turns out that more than 70 people are currently working on this massive mod, from voice actors to artists to coders. Because of the age (and relative low quality) of the resources in the original game as well as the limited Morrowind-style content available in Skyrim already through its official expansions, a vast majority of content like weapons, armor, enemies, and creatures need to be remade from scratch. Even landscapes and environments require significant work, since they diverge so heavily from the snowy slopes and grassy plains native to Skyrim itself.
You can keep abreast of this mod's development (and find out how to contribute your own skills) on the project's site.