There's an unbelievable amount of mods available for The Elder Scrolls V: Skyrim from the obscene and naughty to the absolutely ridiculous and nonsensical. Dedicated fans of the game have even released entirely new lands and stories to rival Skyrim's original in breadth and scope. TESRenewal is attempting to do a sort of inception within the framework of Skyrim's Creation Kit and answer the question, "what do you get when you mod an Elder Scrolls game into another Elder Scrolls game's engine?" The answer they're working on is Skyblivion [official site]. Check out their progress in this new video:
Skyblivion seeks to take the entireity of The Elder Scrolls IV: Oblivion and port it into Skyrim as a mod. That means TESRenewal is bringing all the quests, every NPC, and every location over, and my mind wants to explode at the thought of how tedious it must be to work with such a huge amount of data. The Skyblivion team has continued making process towards their goal and recently released this video showing progress.
As of now armor, weapons, and shields are in the game, NPC's have been manually created, and new textures and models have been crafted to replace some of Oblivion's original assets. The Skyblivion team isn't quite ready for release, they've only just hit version 0.2, but if you want to help make their dream a reality quicker, there is a call out for designers, modders, and other talent to pitch in and help develop the mod.
Those seeking more information on the mod itself, or how to apply to join the Skyblivion team should head to the site. That's also the home of Skywind, the mod bringing Morrowind into Skyrim.