Rak'gol
The Rak'gol are a race of spacefaring pirate/psychopathic-murder-lizard/insect/cyborg... things. These guys are pretty much what happens when the Dark Eldar has all their kinkiness and faggotry replaced by badassary and awesomeness with a slight hint of Rip and Tear! But Games Workshop being Games Workshop, for some reason, hasn't created a Codex for these guys. The majority of /tg/ pray that they will one day receive some added fluff and crunch on these Pirate-Cyborg-Lizard-Insects. Luckily, FFG decided to oblige us.
From what we have learned, the Rak'gol are a species of aliens that like to scavenge and loot things from other aliens. Often their would-be hostages are either killed, tortured then horribly killed, or are sent to areas best not talked about. They (and the Tyranids) are the only race whose origins have not been explored much, due to their first contact being in the outermost reaches of the Koronus Expanse and the fact that trying to negotiate and talk to them often ends with the interrogator being ripped apart and shat upon. Because of this, the Imperium have trouble knowing what the hell these guys are up to. The only time the Imperium actually get a specimen to study, it's a corpse, and the results are often at best inconclusive. Being described as reptilian with some insectoid features, they are infamous for their apparent hard-on for cybernetic surgery, changing their already deadly natural bodies into even more fearsome forms.
Fortunately for the Imperium (or so they say...) the Rak'gol are easily identified by their apparent ramshackle designs of their starships as well as being the only race whose technology is worse then the Orks'. Although their technology is relatively primitive, they make up for this with brutal simplicity of design. The Imperium considers them to be less intelligent than Orks, probably because they seem to lack any sort of language, communicating only in roars and grunts. It's unknown how they manage to coordinate building weaponry, let alone starships, but they seem to manage somehow...
Caste
The Rak'Gol at least show some sign of intelligence, in that they have a clear and specific rank (which is surprising given their apparently bestial nature), and thus they know who's boss of the Pirate Games.
Rak'gol Carvers: Your typical mooks, they look like the triple-bastard love-children of Slenderman, a mantis and a velociraptor. Completely naked (but that doesn't stop them for being tough enough to shrug off Bolters like they were pea-shooters) and terrifyingly vicious. They are only allowed to be gifted with Cybernetics if they survive their first raid, and prove to their superiors that they can rip and tear. They're usually armed with basic stubbers or autoguns, but if they lose them, they can still use their claws, teeth and tails to rip Guardsmen apart like candy-floss.
Rak'gol Marauders: These guys are the most common and easily noticeable Rok'gol during their raids. They're upgraded Carvers (quite literally), and all of them possess a cybernetic feature of some kind. They typically carry Razor Guns or Howler Rifles, but very rarely carry Rad-beam Cannons instead. Often classified as the "Space Marine" of the Rak'gol, while their Carvers counterpart are the "Guardsmen" of the species.
Rak'gol Broodmasters: The captains and leaders of the Rak'gol. These aliens have so much bling and cybernetics that you could actually confuse them for an actual robot. They often tell their inferiors where to hunt and which places boast great opportunities for raiding parties. They also have a lieutenant version called Rak'gol Clutchmasters, which are literally Broodmasters on a diet.
Rak'gol Abominations: As their name suggests, these are some of the highest-taking most hideous members of the species.
They fuse their Cybernetics with Yu'vath technology, making them incredibly dangerous and powerful. They look like the abominable fetus of a Rak'gol Broodmaster and Dr. Frank N. Furter.
Rak'gol Renders: Basically Abominations with extra helpings of RAEG and Rip And Tear.
Techno-Shamans: You ever wonder what would happen if a Rak'gol stole some psykers from the Imperium and infused their powers into their cybernetics? Have you ever wonder ed what they would look like? Well rest assured, the Techno-Shamans are here! They look like they're wearing a Xenomorph head as a helmet and are known to make low-level psykers shit themselves in terror.
Technology
The technology of the Rak'gol is so ramshackle, primitive, and generally poor in quality that it makes Ork designs look ingenious. Yeah, seriously. Their ships are among the few still using nuclear fission reactors in the 41st millennium, as compared to the Imperium's plasma fusion generators. In fact, these aren't even good fission reactors; they regularly leak such massive amounts of radiation that any normal human would be killed almost instantly. This has led the Imperium to wonder just how durable these fuckers are.
The Rak'gol also tend to steal and use technology from other races, including the Imperium. This means that, essentially, they are the xenos equivalent of the Blood Ravens. On at least one occasion, a Xenobiologist misidentified them, because they had stolen so much.
In fact, the only original thing these guys have (and their most famous trait) is their love of cybernetics. After every raid, surviving Rak'gol are implanted with cybernetics, both to improve their bodies and as a sign of status. Most of these are the typical, cliché implants, like arms or legs, but higher-status Rak'gol are gifted with fancy-schmancy rad-weapons or power claws. Despite the primitive look of these implants, they are highly effective, being made to get shit done.
Weapons
It should be noted that most of the time, Rak'gol weapons are stolen Imperium Stubbers and Autoguns, however here are a few weapons considered original to the Rak'gol, even though they look like they can only fire five shots before they're useable only as makeshift clubs (which they're designed to be good for).
Rak'gol Razor Gun: Think of these as an Orkified version of an Eldar monofilament weapon, they are usually modified Autoguns that fire barbed wire in a bullet shape, and are usually seen to rip and tear apart Guardsmen like wet-tissue paper thrown into a wood chipper.
Howler Rifle: Imagine these guns as triple-barreled machine guns built by Haitians... expect carnage, pain and the collateral damage of the "Woopsies, it seems my gun kind of broke apart and hit Jimmy on the eye!" variety. Are noted to vomit out so many bullets that the gouts of flame from the end of the barrels could be re-purposed as a flamethrower.
Rad-beam Cannon: These are essentially masers that shoot out beams of nuclear radiation that somehow "voraciously breaks down armour and materials".
Rak'gol Rad Axe: These are literally power-axes that emit and contaminate the atmosphere with nuclear radiation. /tg/ often imagines them as normal pole-axes with a red light or tinge at the tip of the blade. Damage usually includes severe radiation burns. Nasty stuff.
Rak'gol Intimidator:Nobody knows what they look like, not even the Ad-mech knows what the hell they're meant to be, other then be "Torture Devices" to any poor chap. We like to envision them as needle gloves like Scarecrow from Batman: Arkham Asylum has, but those sick bastards from /d/ like to imagine them as electro-whips used to "torture" captured Eldar women...