"Planet Freelancer" (there are multiple reasons for the quotes, which I'll get to later) is the planet upon which most of the first 10 seasons of Red vs. Blue occur. Blood Gulch, Valhalla, and most of the other locations the characters visit are situated on this planet. The only scenes which are known to take place off-world are the majority of the prequel scenes in seasons 9-10 (and most likely those in Out of Mind) and Wyoming's introductory scene. In this analysis I assume all shots of visible halo rings and the ark, as well as the shot of the exploding ring in season 3, are non-canon.
One Planet or Two?
There is debate as to whether Sidewinder is a location on the planet or a separate entity. Church indicates it as a separate planet in season 1 (although this could be misinformation to convince the simulation troopers that the Red/Blue war is galaxy-wide), and throughout the BGC characters only ever arrive at Sidewinder by teleporter, and are presumably unconscious when they leave it. In season 8, however, Church and Tex are implied to have walked there, and Washington, Maine, and Doc arrive by warthog (albeit a different warthog than the one they left the alien temples in). Season 10 further complicates matters by showing the MOI approaching what appears to be an entirely frozen planet before crashing at Sidewinder.
Whether or not Sidewinder is a separate planet, it is most definitely close enough to be in teleporter range, and close enough that space travel via pelican is feasable between the two but not to other planets. If the freelancers that went rogue at the end of season 10's prequels had access to space travel, there must have been a reason Tex, York, North, South, Maine, and eventually Carolina all ended up on the same planet. The most reasonable theory I've encountered is that Sidewinder is the planet's moon, and while travel to and from can be accomplished via pelican or teleporter, travel to other planets requires a ship with FTL technology, and the freelancers, being war criminals, wouldn't be able to get access.
For a long time, the prevailing theory was that the "simulation planet" was tidally locked to its sun, much like Earth's moon is tidally locked to it. The "light side" of the planet was mostly desert, and the "dark side" mostly frozen wasteland (this fed into the theory that Sidewinder was part of the planet, accounting for the all-ice view of the planet in season 10) This theory was instigated by the sun never setting, as indicated by Grif's line about the sun not setting in three years. In season 10, however, the sun did set, and the night had a presumably short duration. I'm not sure if there is an orbit that would allow for normal-ish nights spaced between several-year-long days.
Another reason that I have used quotes for the accepted titles is that the planet is not exclusively owned by Project freelancer and is also not reserved entirely for simulation bases. Season 10 implies that the Director has to request the bases individually. It is also shown in Out of Mind that the planet contains at least one functioning city, presumably outside the Director's control. There is a definite UNSC presence on the planet, at least after the war, with soldiers working for the then-Chairman appearing in the Recollection. Season 10 includes a UNSC archive center (possibly recycled from PF Command) and the three hornet pilots that attempt to arrest the BG crew.
While it is unclear exactly how much of the Great Prophecy actually had to do with the locations in the BGC, the structures in the desert are definitively named "ancient alien temples" in season 10 and are presumably forerunner due to their appearance and the presence of a monitor. The Great Key may have also been from the planet, however it should be noted that the power station at which it is found is a human facility, and the key could be from somewhere else.
The true nature of the Great Prophecy is only just being revealed in season 13, so this section is by no means complete.
We've been told they're half-human and half-alien.
The alien half consists of the Promethean weapons they look like. It's all alien technology to Charon, and why wouldn't they pick the best of the best weapons of the lot to use for their products? The extremely rare Forerunner tech could also just be more marketable than boring old Covenant tech, both being new and being closer in color and shape to familiar human weapons.
The human half consists of replacement parts and added components, most of which are in the interior of the guns. "Half" doesn't need to mean "split down the middle." Think about it. They're already advanced alien guns, the only reason you would need to add human tech to them would be if it was required to make them function as weapons, which it was since all the alien tech on Chorus was deactivated.
None of the characters in the show would have ever seen a functioning Promethean weapon, and thus wouldn't actually know how they're supposed to function. Charon and everyone else may very well believe they've created something new when all they've done is "fixed" the existing tech to work how it would normally (and in some cases the effect has been modified, such as with the future cubes). The "meddling" with the Gravity Temple was just the same thing, adding human components to get deactivated alien tech to work.
This brings up the question of why there was Promethean stuff on Chorus in the first place, which is really a question of who the creators of the temples/keys are and where they got the Promethean stuff, and that's a headcanon for another day.
So, yeah.Went ahead and finished the MK VI permutations. Because Spiderwash.
Pretty much done with normal MK VI, but still need to work out a few more bugs and make some more hand variations. This is all done in Powerpoint so once I'm done with that and have some weapons rendered I think I might release some files for people to play around with.