Cyborks're quite simply Ork cyborgs, like Imperial Servitors but with their mental faculties (such as they are) fully intact. Some're willing volunteers who wanted some snazz, others were just in the wrong place at the wrong time (for them at least, the Painboy was very grateful). The exact nature of the Bioniks in question varies from individual to individual, as the Meks rarely follow standardised designs, and what the cybork in question gets is more a question of whatever the Dok was feeling like installing at the time they popped in for 'serjery'.
Rogue Trader 2nd edition was, of course, the golden age of Orky research into this branch of the tech tree, with sizable lists of individual custom bionic bitz in the form of Hands, Arms, Legs, Kraniums and assorted miscellaneous bits and bobs collectively referred to as "Dok's Surprises". All of which debuted in "Ere We Go!", one of the two ork splatbooks for the era. This was also when Cyboar mounts showed up as well. This period of rampant innovation was probably spurred on by Painbosses being HQ choices at the time, and thus having the authority to splurge on their pet projects to their hearts' content.
But it couldn't last, as with everything good, and nowadays the only Cyborks you'll see on the battlefield in 9th Edition're the odd one or two Kustom Jobs in a Nobz Mob, plus the Supa Cybork Body Shiny Gubbin. As early as 3rd edition, the various bionikz were all boiled down into simplified rules for easier mob usage, and they only got simpler from there.
In 2nd edition is where all of the crazy different bionik bitz were first introduced, and as such these implants get their own section below. You pretty much had to randomly generate what kind of bionik you got from the five categories (hand, arm, leg, head, surprise) and then generate the precise bioniks.
In 3rd Edition, Cybork Bodies gave a 5++ Invulnerable Save, Bionik Bonces gave +1 to your Armour Save, and Bionik Arms counted as an additional CCW which could unleash a single bonus attack with S4 and I6.
Full Cyborks could be taken as a bodyguard for a Painboss, in a mob of four to nine. They only had Sluggas and Choppas, with no weapons upgrades available at all, but they didn't need them, they'd been upgraded enough. For as many points as an 'Ardboy, a Cybork came with S4, T5, and a 5++ Invulnerable Save. They were the toughest infantry unit in the Codex, though limited in numbers.
Cyboars meanwhile had a 4+ Armour Save and an additional CCW from all the reinforcing plates and spikes, but they tended to be even less intelligent than their unaugmented brethren, and could sometime crash into an inconvenient tree or rock and kill themselves during a charge. Super Cyboars got a 3+ Armour Save instead, and got the Fleet of Foot Special Rule for one turn when the Warboss in the saddle pressed Da Big Red Knob.
in 9th Edition, basic Cybork Bodies give a 6+++ Feel No Pain, the advanced Supa Cybork Body gives a 5+++ Feel No Pain, Bionik Arms've been revamped as Power Stabbas, and the gunner for the Kustom Boosta-Blasta sports a Targeter Eye.
Kustom Hands & Arms
Bionik Hands are the simplest of all the bioniks from Rogue Trader, and simply replace a mangled hand with a random ranged or melee weapon. If you're lucky, this could be one of several Power Weapons... or it could be a clunky blunderbuss.
Bionik Arms is where the interesting stuff happens.
Telescopic Arms grant +2 Initiative in close combat.
Magnetic Arms grant +1 WS and +1 Initiative in close combat.
Squig Attack Arms contain a built-in cage for one of several kinds of attacking squigs, which grant a bonus attack to represent the squig being allowed to pop out of its cage and then bite a victim, or a "stink squig", which can be used to create a cloud of tranquilizer gas around the ork.
Spike Arms are covered retractable spikes or blades, granting +1 WS and +1 Strength.
Grapple Arms can, obviously, be used to make a special grappling attack on enemies.
Grenade Thrower Arms give the bearer increased range with stikkbombs.
Extra Bionik Arms are, well, just that; rather than just replacing the missing arm, the painboy implants a third arm (or a second pair of arms), letting the lucky ork carry more weapons and punch more gits at once.
Finally, there's always the Bionik Arm with Kustom Weapon, which is just a bionic arm with a random Kustom Hand attachment thrown in for good measure.
Bionik Legs can come in either singular or double versions.
Peg Legs are the el cheapo option, and no self-respecting ork wears one if they have another choice. -1 Movement for this.
De-luxe Booster Legs have rocket thrusters installed, giving them +2 Movement. Weirdly, these can be installed singularly and proceed to work just fine, and effectively you can get +4 Movement for having 2 Booster Legs!
De-luxe Kicking Legs are specially modified for use in combat, granting a bonus attack per leg.
Basic Bionik Legs have no special effects beyond letting the ork keep on walking, obviously.
Wheels, Tracks and Hover Units basically double the ork's Movement rate, with the special terrain restrictions for the appropriate kind of vehicle.
Jet-Powered Legs are only installed in pairs, and consist of a pair of vertically orientated jet thrusters. In essence, the ork now has a jet-pack... but can't walk in any way other than by trying to make short, control, jet-propelled "hops".
Special Jumping Legs are spring-based, allowing the ork to make huge leaps. +2 Movement, but must be installed in pairs.
Telescopic Legs are also installed in pairs, and grant both +2 Movement and increased abilities to see and shoot over tall obstacles.
Suction Feet are installed in pairs, obviously, and let the ork walk up vertical and along inverted surfaces.
Finally, the Gyro-Stabilized Monowheel lets the ork race around on a single motorized wheel, which is surprisingly quick.
Any skull or facially based implant is gathered into this section. Non-Weirdboy Orks have a 25% chance of gaining a random level 1 psychic power they can use without psi-points whenever they undergo a Rebuilt Kranium implant. Most of these are kind of self-explanatory.
Telescopic Bionik Eyes make the orks with them better shots over long ranges.
Targeter Eyes, meanwhile, just make them better shots in general.
Respirator Mouthpieces build a gas-filtering device right into the ork's face.
Auto-Senses give the ork enhanced visual abilities, making them impervious to smoke and other blinding effects.
Stainless Steel Skulls are quite desirable, since they make the ork better equipped at headbutting contests.
Stainless Steel Mandibles look flash, but have no actual in-game effects.
Steel Horns are popular because they're even better for delivering headbutts than steel skulls are. They supersede the steel skull implant, so no point trying to take them together.
Lobotomies aren't so much an implant (duh) as a result of the painboy failing to curb their natural desire to play brain surgeon. It turns the victim ork into a Madboy. Too many of these, or the infamous Squig Brain Transplants, and the Dok will get a right kicking from angry orks.
Periscopes are... well, they're periscopes. They give their bearers the ability to see things from further and to look around without putting themselves in danger. Their bearers are often outfitted with rokkit launchers or similar ordinance, due to their increased ability to check range and aim.
Explosive Craniums, despite what you might think, are actually sometimes requested! The idea is that the dok plants an explosive in the ork's head that detonates when the ork dies, which appeals to the ork's sense of vengefulness.
This is the catch-all terminology for any orky bio-mod that doesn't fall into the above.
Fuel Injection Implants outfit an ork with a refillable tank of fungus-juice fuel and the ability to flood their systems with the stuff via intravenous injection. It's basically an orky stim-pack, wich can be triggered to gain +2 Movement and Initiative for the rest of the game.
Fungus Breff implants are basically secondary stomachs laced with symbiotic fungi, allowing the ork to belch gouts of toxic gas in combat.
Iron Masks are extensive cranium reconstructions; steel teef, built in helmet, and three random facial bioniks all in one.
Cybork Bodies are the term used for heavy cybernetic reconstruction of the torso, making the ork stronger and tougher (+2 to both scores), but also prone to malfunctioning like any other bit of ork engineering.
Head Grafts are what happens when a painboy sews a still-living decapitated ork head to the body of an otherwise intact ork. The two heads share control of the body, gaining increased ambidexterity. On a 5+, this implant comes with a second pair of arms for free, allowing the ork to wield four weapons at once thanks to its twin brains and augmented nervous system.
Armor Plating is simply what it says on the tin; grafting metal bits to the ork's skin and flesh to patch up holes and make them tougher (+1 Toughness, in fact).
Steel Teef are a cosmetic treatment that no ork wants. For reasons that should be obvious if you read the Toof article.
Finally, the infamous Squig Brain Transplant results when the painboy swaps the brain of an ork with the brain of a pet squig, creating a zombie-like orkish slave. Too many of these will get a painboy krumped dead quick! Squig-Brained Orks have M4, WS3, BS2, S6, T6, W2, I2, A2, LD3, Int 3, Cool 8 and Willpower 3.