From the website:
So, what is Halo Reborn?Halo: Reborn is an upcoming custom Halo Campaign that aims to follow the events of the Halo trilogy but retelling its story through an entirely new context with new and updated missions, environments and encounters in one unified experience. That means in one engine, one game, and as of now you'll be playing Halo 1, Halo 2 and Halo 3 entirely in Halo 3 as one continuous story.
Halo Reborn mod for Halo: The Master Chief Collection
Halo Reborn is an upcoming custom Halo Campaign that aims to following the original Halo story but telling it through new environments and layouts to provide a fresh experience to the player.
www.moddb.com