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,
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.

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 firearms are weaker than the recommendations from the DMG.

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.