enderal looks fascinating

enderal.com

is offering a free game that requires a working installation of Skyrim.

You can go to their website and download the files.

Enderal is a total conversion for TES V: Skyrim: a game modification that is set in its own world with its own landscape, lore and story. It offers an immersive open world, all for the player to explore, overhauled skill systems and gameplay mechanics and a dark, psychological storyline with believable characters.

Enderal is free and can be played by anyone owning a legal copy of TES V: Skyrim. (No DLCs are necessary.) It is developed non-commercially by SureAI, the team behind the renowned Oblivion mod "Nehrim: At Fate´s Edge" (and various other projects).
Features:

An open world with its own lore and hand-crafted, detailed and diverse landscapes (desert, heathlands, forests, jungles, mountains and more)

An unconventional story with psychological and philosophical undercurrents

German and English localizations, both fully voiced by dozens of speakers, many with a professional background

Multi-faceted, believable characters with own ambitions and motivations

Overhauled gameplay with experience points, survival mechanics and hard, challenging combat

An overhauled skill system with classes and new special abilities

A housing system allowing the player to design their own homes

30 to 100 hours of expected playtime