The development of Halo: Combat Evolved actually is a pretty remarkable story and at one point it was an RTS intended for Apple formats, and later also a third-person title. As you might imagine, this means that before it eventually was released for Xbox as the brilliant FPS we know and love, a whole lot of content had to be scrapped.
Now 343 Industries and the mod group Digsite is working on a project to restore some of this previously unseen Halo content that was developed by Bungie, and some of it is coming to Halo: The Master Chief Collection:
"We went deep into the archives and uncovered Milestone builds of Halo PC which had material that never made it to the retail release. Of particular interest to us were design/production docs, Bungie feedback notes, tags, compiled maps, and source data for previously unseen multiplayer maps.
Some of these were cut before they even had a name more evocative than gbx_map#. Nevertheless, two were interesting enough to playtest and bring over the finish line within MCC."
It was also discovered that Gearbox (who made the PC version of Halo: Combat Evolved) also had unused content, that will will now see the day of light over 20 years since it was scrapped:
"Gearbox had made a bunch of brand-new textures that were not being used whatsoever. I felt it would be a shame if these textures never got used, so I decided to remix Indoor into a brand-new map that could better utilize these newfound bitmaps."
There's still a whole lot more to discover, and if you are into Halo and/or video game archaeology, head over to Halo Waypoint for a pretty interesting story, and there is more to come.
Thanks, PCGamesN.