Oh my god! How did I not know about this!!! For the last decade (and is still being worked on even now) there has been an amazing huge fan made total conversion addon to Command & Conquer Tiberian Sun called Twisted Insurrection!
This stand alone addon takes place in an alternate timeline where NOD won the original C&C1 Tiberian Dawn story taking control of GDI’s Iron cannon and conquering the world! Twisted Insurrection adds a huge new 50+ mission campaign, completely overhauled GDI & NOD units and buildings, a new third faction called GloboTech, new terrain and tiberian types, huge city maps (RA2 style), underground/inside base building infiltration maps (RA1 style), amazing brand new cutscene videos, and a huge new soundtrack of 70+ songs including one from original C&C & Red Alert composer Frank Klepacki! And if all that isn’t enough they’re now working on adding the entire original Command & Conquer 1 Tiberian Dawn campaign game into the Tiberian Sun engine with enhanced/overhauled versions of the original buildings and units!