One of my free rpgs, published in German, is Freeway Warrior.
It’s a Mad Max rpg that uses d20 exclusively. As you might have guessed, the system is very Arnesonian, roll 1d20, high is good.
It’s pure old school, using lots of tables for character generation and other stuff. You can even roll up your vehicle.
One thing I’m really proud of is the vehicle combat system I developed for Freeway Warrior:
Here’s the text (autotranslated by Deepl because I’m really lazy today):
In the fight man against vehicle or vehicle against vehicle we distinguish between light and heavy weapons.
Light weapons are those that a person can easily carry with one hand: Guns, submachine guns, light machine guns, oil sprayers, smoke candles and so on.
Heavy weapons are those that a person can only carry with difficulty or not at all with two hands: heavy machine guns, on-board guns, cannons, minelayers, rocket launchers, and so on.
Now you could simply give a vehicle a number of hits and then use the normal fighting rules. That would be possible, of course, but we find it boring. The distinguishing moment in vehicle combat, in my opinion, is that a single hit — the decision-maker, the kill — decides the fight.
Therefore we introduce in the following the hit matrix for the vehicle fight. The upper line indicates whether the shooter shoots at a vehicle with a light or heavy weapon. In the left column you can find the types of vehicles to be fired at. Where the weapon and vehicle types cross, you find a number. This is the number that a shooter must roll at least on the D20 to make the kill — the hit that paralyzes the vehicle –.
If the referee wants to make a vehicle particularly robust, he can also increase the number of required kills from 1 to as many as he likes.
Characters who can shoot well are allowed to roll the dice again if they fail.
Motorbike, Ultralight Aircraft: light weapon 15, heavy 10
Small car: light 16, heavy 12
Sedan: light 17, heavy 14
SUV: light 19, heavy 15
Light truck: light 20, heavy 16
Truck, Zeppelin: light 20, heavy 17
Tank: light 20, heavy 19
If a character scores a kill, he rolls 1d20 again. 1-16, the hit damaged a part of the vehicle so badly that it is no longer possible to continue. 17-20, the driver was hit.
KILL — which part of the vehicle was hit?
1-2: tire, apron, track, gasbag
6: fuel tank or battery
7-10: chassis, undercarriage