Modders have been making tweaks to PC games for years, adding items, fleshing out existing content or creating completely original experiences. The Elder Scrolls games have been particularly well known for their dedicated modding communities, but I think they have out down themselves with Enderal: The Shards of Order.
Enderal: The Shards of Order is an incredibly ambitious total conversion of Skyrim, creating a brand new experience with new locations, a brand new story and thousands of secrets. What’s even more impressive, is that it is actually a sequel to modding team SureAI’s total conversion mod for Oblivion known as Nehrim: At Fate’s Edge, one of the game’s most popular mods.
You can checkout Enderal: The Shards of Order and follow its progress over on its Moddb page, which was recently nominated as one of the sites top 100 mods of 2014. The mod is on track to releases sometime in 2015.