I have issues with how games like Shadowrun and Cyberpunk 2020 handle the mechanical tradeoff between augmentations and being made of the meat you were born with. Some sort of abstract degrading "humanity" stat brings a whole host of philosophical questions into play, with answers that either constrain the thematic space of the game to TECH = EVIL or are just plain ableist (people with prosthetic limbs are less human? please stop). Some newer games, like Hard Wired Island, make the downside of tech explicitly that it's expensive - and while that's miles better, it's still not particularly satisfying to me, because even under Fully Automated Luxury Gay Space Communism there's still gonna be some sort of tradeoff.
Here's an alternative: tech is complicated! Anyone who's worked with intensely customized systems, built their own PC, compiled their own Linux kernel (please don't nitpick my incredibly limited Linux knowledge in the comments), or just had to check the side effects and interactions of multiple medications knows that this shit is difficult and often requires compromises just to stay functional. When you're fitting a bunch of electronics directly into the human nervous system, you combine the most complicated parts of all of the above, and glitches are bound to emerge.
Stuff that doesn't need any extra neural integration to work and just runs off of existing wiring - like prosthetics and cosmetics - doesn't strain your system in this way. They've ironed out those kinks. Anything that gives you superpowers, on the other hand, is annoyingly buggy and high-maintenance.
Cybernetics Rules
Every cybernetic augmentation has a Strain level. When you're making a check with your augmentations, roll an additional d20 for Compatibility. If you roll under your total Strain, you Glitch. There's a variety of ways to compensate for Strain, including compatibility-forcing drugs like Neuropozyne, buying all your augs from the same manufacturer, or spending hours upon hours each day reconciling patches and bugs before they fire.
For the less technically gifted, or merc in a rush, Neuropozyne is a highly-addictive prescription drug tightly controlled by major pharmacorps. Each dose allows you to ignore Compatibility rolls when using one aug of your choice for 24 hours by selectively overclocking your nervous system. Make a CON save vs. chemical addiction after every use; being weaned off of it safely is a complex process that requires a month of professional monitoring and temporary augmentation removal. When in withdrawal, your Strain is doubled.
Neurachem is the bleeding-edge black clinic upgrade to Neuropozyne, with all the brakes removed. None of your augs will Glitch on neurachem, and the world looks like it's moving in slow motion. You get to react before anyone else does, and can do the thing from the Matrix where you dodge bullets. You're an augmetic god. When you come down from a Neurachem high, your base Strain goes right to 20, and make a Glitch roll for each aug you activated while on it. Also has all of Neuropozyne's side effects.
If you want a cyberpunk game with magic, tech, and a fundamental irreconcilability between the two, force a Strain roll on casting in addition to Mishaps, and a Mishap roll on aug use in addition to Strain. Need a justification? Both magic and augmentations interact with the human brain in increasingly complex and nonsensical ways, and feedback from one can break the other.
Glitches! If your Compatibility roll is under your Strain, that result happens.
1. Update Required. +1 Strain until you spend an hour installing a mandatory update.
2. Input Lag. Anything you're doing with this aug happens a second later than you expect; make your roll again and take the lower result.
3. Memory Leak. This action takes twice as many resources (time, bullets, power, etc).
4. Low Battery. You've got d4 more uses before you need to plug into a power source and recharge this aug.
5. Malfunction. The aug does something harmful to you instead of functioning as intended.
6. Null Pointer. Make your next Compatibility roll at disadvantage, but if both are under your Strain take the higher result.
7. Reboot. After the action, your aug shuts off. Takes a minute to boot back up.
8. Crossed Wires. Another random aug activates instead of the one you meant to.
9. Shutdown. Action fails, aug shuts off. Takes a minute to boot back up.
10. It's Not a Bug, It's a Feature. Your action goes awry in a way that's entirely outside your use case. Future similar actions malfunction in the same way, until you spend an hour finding software that actually works for you.
11. Sensory Feedback. Your senses glitch and fuzz. Disadvantage on all rolls until you take a turn to clear your sensorium.
12. Crash Override. You can't turn it off. Until you spend a turn engaging the manual safeties (you do still have those, right?), it does what you just did every time it has a chance to.
13. Cascade Failure. An additional aug activates and immediately Glitches.
14. Burning Chrome. Take d6 fire damage.
15. Drivers Crossed. Two of your augs swap functionality; or at least they try to. Until you spend an hour debugging, they'll try to replicate each others' functions to the best of their ability (read: poorly).
16. Structural Failure. The hardware cracks as it spirals past its breaking point. Make all actions with this aug at disadvantage, and when it glitches again, it becomes entirely nonfunctional. It needs to be repaired by a professional.
17. Implant Ejection. The augmentation you're trying to use forcibly disconnects from your body to prevent lethal biofeedback. Lose all functionality it provides until it's reinstalled by a doc. If external, it literally falls off.
18. Dataclysm. Neural strain sends your consciousness careening through the augs' bioneural output logs. Save or forget the last d6 hours.
19. Total System Collapse. Biofeedback shorts out your autonomic nervous system. Fall unconscious.
20+. Count Zero Interrupt. Your augmentations have reached the breaking point of complexity where they develop their own alien consciousness and override your entire brain. Save vs. death. If you fail, you die, and become an NPC under the GM's control, a cyborg intelligence with an entirely alien value set puppeting your shambling metal-studded corpse.
Sample Cybertech
Cosmetic (0). Vidtats, plastic surgery, reskins, etc.Cyberlimb, Prosthetic (0). Limb replacements that replicate basic human capabilities. Getting extra functional limbs requires them to be Enhancile.
Cyberorgan, Prosthetic (0). Organ replacements that replicate basic human capabilities. Any human organ can be replicated, besides the brain. Getting extra functional copies of organs requires them to be Enhancile.
Cyberlimb, Enhancile (1+). Limb that goes above and beyond baseline capabilities. May Glitch when enhancile capabilities are used. Baseline stats are identical to those you started with; your musculature can only handle so much without extra reinforcement.
STR+ (+1 per 3 STR over baseline). Maxes out at 18. Only applies to actions taken with this limb.
DEX+ (+1 per 3 DEX over baseline). Maxes out at 18. Only applies to actions taken with this limb.
CON+ (+1 per 3 CON over baseline). Maxes out at 18. Only applies to actions taken with this limb.
Detachable (+1). Can be removed and remote-controlled. When detached/reattached, or enhancile capabilities used, may Glitch.
Disguised (+1). Looks like a normal meat arm, no matter its capabilities. When scanned, may Glitch.
Extra (+1). This limb is an extra one, in addition to the base 2 arms 2 legs that humans tend to have. Comes with the necessary firmware and extra neural connections to make control as easy as your first set of limbs.
Inhuman (+0). Tail? Tentacle? Crab claw? This limb doesn't follow the two-segment-and-hand/foot plan that your brain expects.
Integrated Toolkit (+1). Built-in tools for a profession of your choice. Modular.
Telescoping (+1). Can extend up to 4x as long as default with no loss of capabilities. When extending/contracting, may Glitch.
Datajack (1). Universal mind-machine interface socket and wire. Plugs into brain stem or prefrontal cortex; allows for direct neural input to external electronics (bypassing manual controls). Actions with plugged-in equipment have chance to Glitch.
Eidetic Storage (1). Records sensory data and stores it in internal databank wired to the medial temporal lobe. Recalling this data may Glitch.
Gecko Grip (1). Smartly deploys from hands and feet to create almost-unbreakable connection to any surface not specially treated with FricFree (tm). May Glitch on activation or deactivation.
Implant Weapon (1+). It's a weapon built into your biology. Follows rules in the system; I'm not providing my own weapon rules in this post.
Blade, Claws (+0)
Pistol, SMG, Taser (+1)
Rifle, Shotgun, Chainblade (+2)
Sniper Rifle, Flamethrower, Rocket Launcher, Typhoon System, MASER, etc. (+3)
Disguised (+1). This weapon is concealed with a set of articulated joints inside your body. May Glitch when extended. Only usable when visible.
Muscle Replacement (1 per area). Meat? We can do better. A bundle of synthfibres replace your muscles in an area. You get advantage on STR tests with that area. The areas are all 4 limbs and your torso. Doesn't stack with cyberlimbs.
Pocket (1). Hidden skin pocket holds 1 inventory slot of items inside a scanner-proof container disguised to look like medical augs. May Glitch when scanned, or opened.
Cyberorgan, Enhancile (2). Replaces any internal organ besides brain. Advantage on checks that involve that organ, but may Glitch.
Dataeyes (2). Lets you interface with the internet and data without a physical connection. Acts as smartphone, but also visualizes nearby wireless connections and networks. When using downloadable filters like infrared, telescopic vision, flare compensation, UV, etc, test to Glitch.
Drug Dispenser (2). Contains a week's supply of any medications you can acquire, and dispenses them on command/automatically. Gives you a Glitchy save against any side effects you wouldn't otherwise be able to save against (except for Neuropozyne and other augmetic drugs).
Morphkit, Facial (2). Lets you change your facial features to anything within human-baseline (or reasonably beyond) on command. May Glitch on face morph.
Pain Editor (2). You can ignore stat damage from minor wounds for up to 10 minutes. May Glitch when you take a wound.
Sense Suite (2). Total overhaul of your entire sensorium. You're aware of everything that happens around you within 10 meters, and can focus on a point up to 100 meters away to be fully aware from there. Focusing may Glitch.
Armorskin (3). Layers of plating replace your skin. Sets your base AC to 12 or greater, at the cost of being Wounded also potentially causing a Glitch.
AC+ (1 per 2 AC over 12)
Disguised (1). Looks like normal skin, no matter how much AC it gives you. When scanned, may Glitch.
Resistant (2 per elemental damage type). Your skin also is insulated against 1 elemental damage type. Damage dice of that type are rolled against you with disadvantage.
Attention Coprocessor (3). Gives you the fabled ability to consciously multitask with no loss of function. You can do 2 things at once with no penalties (besides potential Glitches), so long as it's physically possible to do them at the same time. You can have multiple Coprocessors installed.
Camoskin (3). Lets you change your skin color and patterns at will; also lets you set it to auto-camouflage into your environment. Auto-camo may Glitch when activated or when scanned.
Heuristic Optimizer (3). Draws from a wide database of proven heuristics and solution sets, then integrates them into your cognitive problem-solving routines. When solving logic problems, math problems, or getting a quick procedural solution that doesn't require intuition or emotional judgments, you can just automatically solve it with a chance of Glitching.
Microexpression Controller (3). Your expressions and reactions are automatically calibrated to convey exactly what you want them to. You can't give away information from physical or vocal cues, and you can test with a chance of Glitching to read someone else's microexpressions to see unintended subtext.
Bone Lacing (4). In an involved procedure, your bones are sheathed in a composite alloy that makes them incredibly tough. +2 AC, and step down the damage dice of bludgeoning and slashing weapons against you. When recovering HP, may Glitch.
Move-By-Wire (4). Neurons? Too slow. Your nerves have been pulled out and replaced with fibre-optic wiring. You can take an extra action each turn; whenever do you have a chance of Glitching.
Rocket Feet (4). You can temporarily fly for 5 minutes before recharging. Fuel cartridges for your feet are incredibly volatile, though not uncommon (it's like a fusion battery for cars). Activating your rocket feet might Glitch.
Morphkit, Full (5). You can shift your physical appearance to anything within human baseline. This takes 10 minutes of careful alterations, and has a chance to Glitch. If you shift more than once in the same day, the additional shifts automatically Glitch.
Nanoforge (5). An implanted nanohive flash-prints tools and other items you need to your specifications. With an inventory slot's worth of feedstock, you can roll a d6 to craft a mundane, non-electronic item out of that stock. It has a chance to Glitch, and the result of the d6 roll determines how well it fits your specs (higher is better).