A listing for something called Halo Bootcamp has popped up on the Korean Game Rating Board on Tuesday, mentioning both Halo 3 and "PC online game," with Microsoft listed as the publisher. Despite the description, Microsoft has yet to confirm just what Boot Camp is, or might be. However, they did confirm that it is a legitimate project, which is unusual for the company. A spokesperson said only that, "It is not related to our Xbox One efforts, or the Reclaimer Saga, but rather a project we're very enthusiastic about and will have more to say about in the near future."
So nothing to do with the Reclaimer saga would cancel out Halo 5. And as far as a PC port for Halo 3 goes, the last word from Microsoft on the matter came back in March, when a spokesperson told Eurogamer, "We currently do not have plans to release any Halo titles on Steam, nor do we currently have plans to release a PC version of Halo 3."
Bootcamp, according to the listing, is a third-person shooter, which seems to discredit the idea of a Halo 3 port. As such, it's odd to figure why the game is even mentioned in the first place. There's also some mention of online play.
From the title alone, it sounds like it could potentially be a prequel for John-117, his time before he was the legendary Master Chief, or maybe just what sort of training UNSC Spartans had to go through. One theory that was presented was that it could have to do with a spin-off novel, "Halo: Fall of Reach: Boot Camp," by Reed Ruiz. That, or maybe they're already gearing up for some spin-off from the upcoming live-action TV series.
Whatever it is, we'll keep you posted as more information is released.