I spent some time recently looking at how many 5e compatible core rulebooks there are for modern and future settings. I wanted to know how many of them are filling in the rules not covered in the 5e SRD and what OGC worked best for the Steampunk and Science Fiction settings we’re working on. The draft is ready for some comments.

Here are, in alphabetical order, a survey of 5e core books on DriveThruRPG and also one I found on Amazon that did things a little differently.

Core Rules	Genre	Mechanics	=/= D&D	Sales
Advent Horizon
Amazing Adventures	Pulp Adv	Costume Armor, Firearms, Gadgets, Vehicles, and Driving Rules
Dark Energy
Dark Matter	Sci-Fantasy	Mecha & Vehicles are Ships, have Mega Hit Points 100hp		Gold
Delta World	Post Apoc
Entromancy
Esper Genesis	Sci-Fantasy	Firearms, Ships, Vehicles
Everyday Heroes	Modern	Kaiju, Mechs, Vehicles, and Driving Feats
Genefunk 2090
Ghost Ops	Military	Firearms
Shooting Iron	Western		5e & 3.x mix	Amazon
Spaceships Starwyrms	Sci-Fantasy	Ships		Gold
Spy Game	Spies	Firearms, Vehicles
Ultramodern Redux	Modern	Firearms, Mecha
WARPS

Amazing Adventures has a 20-level Gadgeteer that is both similar to and different from Dark Matter’s Gadgeteer. Gadgeteer gets a Jury Rig temporary repair ability. AA has suggested costume AC bonuses and armor bonuses from a leather jacket to Riot/Military Armor, the costume stuff looks better for Pulp. The On the Fly Gadget system seems cool but relies heavily on copying existing spell effects. The long rest, short rest, and unlimited part of the gadget system might be too conservative. A Jetpack is a Flying Gadget, Parachute which emulates feather fall could be normal equipment. The Tesla Coil gun using Lightning Bolt should be limited to once per, according to the gadget system, which keeps it on parity with spellcaster spell slots.
The gadget guidelines, which could be streamlined, are these:
1. Gadgets can’t emulate spells above 6th level, without a 16th level super science class ability.
2. Gadgets can’t normally emulate spells above half the gadgeteer’s class level, on parity with spellcasters. GM may allow no more than one gadget to be above the level limit.
3. A gadget that emulates your max spell level (half class level) can only be used once per long rest. A gadget that emulates half or lower than your max spell level may be used once per short rest. You can buy the gadget again at full cost to reduce the recharge time from long to short and short to unlimited. You must be one level above qualifying for your max level spell gadget before you can buy the second gadget to change the use to short rest. At three levels beyond the minimum, they can buy another gadget and change short to unlimited. They give an example of a 13th-level gadgeteer buying an unlimited lightning bolt gadget (2 gadgets?) as some loophole instead of buying three gadgets progressively starting at 5th.
4. A Tesla Gloves that substitutes a shocking grasp is unlimited, right from the start, which keeps it on parity with spellcasters, firearms, crossbows, etc.
5. GMs can place further restrictions on gadgets such as cool down periods or limited charges and reload requirements
6. Gadgets have to make attack rolls, even when based on auto-hit or area effect spells.
7. Some spells can’t be made into gadgets, examples are wish and raise dead, Victor Frankenstein would like to have a word with them about the last one.
8. Some spells, such as cures, might be further restricted, and if a spell requires a spell component cost, the gadget does too.
9. The GM should impose penalties if the player calls the gadget by its spell name and not its in-world gadget name.
Amazing Adventures has a Hold action in addition to Ready and some extra notes on Help from multiple characters.
Amazing Adventures has three pages of variant Cinematic Unarmed Combat rules.
Amazing Adventures had two pages of Firearms rules under Ranged combat.
Amazing Adventures has five pages of Vehicle Combat Rules.
Amazing Adventures Vehicles have stat blocks comparable to the ones in Avernus and add an Acceleration number. Vehicles have Damage Resistance Bludgeoning but not a Damage Threshold, such as in Avernus or Spy Game. All speeds are in miles per hour, unlike the other two games listed.
Amazing Adventures Madness rules go beyond the SRD and include several pages: Sanity ability score, Insanity treatment, and a Forbidden Lore skill.

Dark Matter has a mechanical race, a Gadgeteer class, and starship rules. DarkMatter’s Gadgeteer gets Experimental Armor, an AI companion, and Overcharge, similar to Starfinder’s Mechanic.

Everyday Heroes doesn’t use armor the same way as 5e, and the firearm damage is weaker than the recommendations from the DMG, which isn’t necessarily bad, just something to remember as they also incorporate automatic fire rules, which increase damage.

Shooting Iron uses 10-level D20 Modern classes with static progressions and class abilities like weapon focus and specialization that add to their to hit and damage as well as other modifiers like point-blank shot. These don’t line up with 5e classes and proficiency bonus.

Spy Game has Unarmored Defense which grants AC equal to 10+Dex Mod + Wisdom Mod starting at 11th level for the Face class. There are Light, Medium, and Heavy Armors plus Shields in the Spy Game.
There are Gadgets that are not the kind made by Gadgeteers but the kind ubiquitous to the spy genre.
Vehicles, chase, and combat rules. Vehicles have a crappy combat speed that is scaled to make characters on foot competitive. The vehicles have many of the same stat block entries as the ones from Avernus, but not all.

A Note on Vehicle Stat Blocks: There was a lot of outcry when the Spelljammer ships came out that they didn’t have the big block of immunities that the vehicles from Avernus had. Others of a differing viewpoint felt that as objects, the immunities to poison, psychic damage, and the like were obvious. Instead of listing them all in each stat block, they should be referenced like construct or undead immunities and save the page count. Rich Redman’s Thunderball Rally rules had both Acceleration and Maneuverability considered for each vehicle, a motorcycle, sportscar, and bread truck should not all have the same ability around a race track. Some of the systems presented use the lesser of the Vehicle or Driver’s Dexterity score for the Maneuverability, and others present an acceleration number.