Enderal: Forgotten Stories is an ambitious total conversion mod for Skyrim, with an entirely new plot and significantly tweaked mechanics. Its creators were previously responsible for other Elder Scrolls mods like Nehrim for Oblivion, but are now moving on to a commercial project, which they say "will hopefully be announced this year."
SureAI, the German studio in question, announced this in the final set of patch notes for Enderal. The patch fixes some problems like a talent not causing the right amount of damage and bows sometimes disappearing when dropped, as well as a few typos.
The modders note that moving on from Enderal means they won't have time to patch it further, or port it to Skyrim Special Edition. You'll still need the "Oldrim" version of Bethesda's RPG to play Enderal.
Though it won't show up in the search bar these days, the original version of Skyrim still has a hidden store page. Enderal is available through Steam as well. If you'd like to know more about what it's like to play, here's a report on its first 20 hours from back when it was first being translated into English in 2016.