Sanity systems have featured in a lot of games. The easiest example is of course Call of Cthulhu, where you're much more likely to go completely insane than actually die of anything. In Call of Cthulhu, beasies and terrible things can strip away your sanity points. It essentially treats sanity as hit points for the mind, save that it's much harder to recover from.
Dark Heresy treats it much like the same way, using a nearly identical system. You gain insanity and eventually get removed from play when you have too much. On reaching milestones or when failing rolls against terrible shocks to the system, you might have to roll on a chart and do some random thing for a while. There are some lasting effects, with characters gaining various mental illnesses, and it's almost impossible to recover, but that's lethality for you.
A few video games have tried for the sanity angle as well, though the vast majority do it poorly. I never knew going crazy meant you got a wavy filter over your eyes, but that's what most games are telling me. Others try to play the player, like Eternal Darkness, and that's at least more entertaining.
The how and why of including a sanity system into Warhawks came into play at about the time I was considering turning it into Cthulhutech. This is also why psychic powers got included - they're pretty important for Cthulhutech. But I didn't want to just have 'mental hit points'. There had to be more that sanity could do, right?
For the actual sanity system itself, I decided to use my normal damage system as a base. You take mental stress, make tests against how much stress you have, and get Insanity Points when you fail (and then erase the stress). But it clearly can't remove dice - physical damage is removing dice already. So what can Insanity Points do?
They can take control away. When you gain an Insanity Point, your character snaps. When creating your character, you choose a psychosis for them, the way they act badly under stress. Maybe they turn Sadistic, or Cowardly, or Psychotic. On receiving an Insanity Point, you are immediately affected by it and act on your psychosis. Every session after that, the GM can force you to act on your psychosis once for every Insanity Point you have. You can recover from Insanity Points over time, but if you ever have four at once, you're out, hopelessly insane.
It's a fairly easy system, and it lets the player keep control of the character. There's not really any randomness to it, but it can still screw the character over if they have to play nice.
For various reasons, I further decided that using psychic powers (and the effects of some psychic powers, especially ones like memory probing) cause mental stress. This serves as a limit on psychic powers, without being too... limiting, I guess. As long as you push it and drive yourself crazy, you can use a lot of psychic powers in one sitting.
Additionally, I wanted to include an extra effort type of thing that characters could use for extra actions, more movement, and so forth. Like how Hawks can give themselves instability for bonuses. It uses much of the same ideas, but instead of instability gain, you choose to take either damage or stress.
As a side note, maybe next time I'll discuss the ways games limit abilities like magic. There are a lot of ways to do it and it's an interesting topic.
And now I'm finally going to talk about guns. Immediately on getting to the point where I needed to outfit characters I knew I didn't want to have to actually stat guns on my own. There are a shitload of different guns in the majority of modern settings, and for good reason - there're a lot of different types of guns in the real world, and those more familiar with firearms have strong opinions on the differences and comparisons between even quite similar weapons.
Plus I really didn't want to stat out like a dozen guns. So I decided to take a different option. Weapons have stats, right? Well so do people and mechs. So why can't you build a gun like you'd build a person?
Working from that idea, I figured out the things I'd need to really stat out guns well. Damage and range are obvious, as are accuracy and rate of fire. There's also the size of the weapon's clip (which is really just how many times you can use it before reloading). And to round it out, the miscellaneous properties a weapon can have, like a blast radius or being nonlethal.
I also wanted to keep things simple and in-theme. As people and mecha use four stats, I could also give guns four simple stats. I decided to divide them up as:
Bullets: Clip Size and Rate of Fire
Barrel: Range and Accuracy
Special: Special Properties
Each gun gets a number of points which, on creation, are distributed among those four stats. A pistol has only a few points, but is easy to use and can be duel-wielded. A rifle has no special properties and gets a medium amount of points. A heavy weapon can't be used on the move and is slow to reload, but gets the most points. Nice and easy, and it covers everything from a pocket pistol to a machinegun to a rocket launcher.
As for how each stat works, Caliber, Bullets, and Barrel all function the same way - they directly improve something, then at every third point in them improve a secondary thing. For example, Damage starts at 1d6 when you have 0 points in it. 1 point is 1d6+1 damage. 2 points is 1d6+2 damage. 3 points it goes to 2d6, then at 4 it's 2d6+1. Special is the odd one out, and is just basically a list of choices, and you get a pick for every point you have in Special.
So now that I've finally explained guns, you can see that I am very lazy and hate statting things.